Idle Problem in Drive Only - Stumbles, Shakes

okay here it goes, when in park every thing is beautiful smooth, just a little rattle from my SC coupler i presume, but when i am in Drive at idle with the brake on i my car shakes, once i'm over 1k rmps it goes away, also it is a little less noticeable in revers than it is in drive, anyone have an idea about whats going on?

EDIT- saw the other forum, checking the motor mounts now

Sounds like your TCC solenoid could be stuck (on) as a possibility. Does it shift very hard 1-2 and 2-3? Do you hear/feel the TCC engage in 3rd or 4th gear?

No it shifts perfect, i can barely feel it, at speed one would think it was a brand new riviera.

could be a crack in one of your vac lines. or a dirty IAC valve or throttle body.
i would check all the vac lines, then sea foam the top end, then pull the TB screen out and manually clean behind it as far back as possible.(i usually remove the TB off the car, but that requires alot more work) Remove the MAF and IAC and clean both of those. at the very least, your car will have better throttle response and should idle smoother. (provided the sea foam doesnt foul the plugs, in which case you may want to drop in a fresh set of AL605's) should only cost you $10 for the cleaners and an hour or 2 of time. plus $8 for new plugs if you go that route.

new fuel filter is a good idea too if you havent done that yet.

Mr.Riviera wrote:

new fuel filter is a good idea too if you havent done that yet.

A good idea in general but shouldn't have any effect on idle if it's driving fine otherwise.

Sounds like motor mounts.

If you can block/brake the wheels, then after setting emergency brake and gettign wheel chocks in place try (at your own risk) this:

- open hood
- put car in gear and watch engine

if it bucks more than a little bit you should suspect your motor and/or transmisison mounts are Wacked.

Albertj

Well,shortly after buying my car I noticed that it idled a little rough while in drive and with the brake applied at a light.It was sooo minimal that I didn't worry too much about it.I changed the fuel filter,put in a k&n,and cleaned the MAF.Next up I was going to do 605's and plug wires (both of which I have already purchased).
I ended up reading through all of the service receipts the previous owner gave me when I got home after buying the car and noticed a couple of visits to the shop for a misfire in cyl #3.The shop states in their notes that they swapped coils and noticed a minimal improvement,then proceeded to change all of the plugs and put in new wires.After that they stated that the misfire was further improved to the point of not setting off the service engine light.However,they noted that after a (running) compression test that cyl#3 was low which possibly indicated a bad valve or carbon build up...or a bad cam lobe.Where as a STATIC compression test showed all cylinders as healthy.
To the point...recently my my service engine light has been randomly coming on and shutting off for a few days,then coming back on.So I took it to the mechanic (which I have an appointment with tomorrow morning for the front struts) and had his boy hook up a scanner since the light happened to be on today.Result??MISSFIRE on #3!!! Along with possible dirty O2 sensors,AND MAF sensor,oh yeah,also a lean reading on (bank 1)??
Damnit!! I just bought this car,and it's so clean you could eat off it,and runs like a freaking bat out of hell!The only thing noticeable is the little stumble at idle in drive while stopped at a light.It is not hardly anything...
So,what the hell do you guys think it could be??Do these cars have a history of eating valve or what?Could it be as simple as a coil??I pulled the 3# plug and it looked clean to me.Very nice as a matter of fact,a nice light tan color. I know the LIM gaskets have never been changed (125k miles).However there is no trace of antifreeze in oil,or vice versa.There is MILD oil weepage limited to the area around the lim bolts at the front passenger side...but again NOT major.
Worst case scenario,the valve(s) in #3 are bad. I would rather do a valve job on both heads at one shot.That being said,the cost after machine work and labor I am assuming is going to be quite high (2500-3000?).On a motor with 125k on it should I just spend a few more grand and replace the whole damn engine??!!Then what the supercharger too??!!
I'm REALLY PISSED AT THE MOMENT!!! I like this car and I do not have the money to buy another used car with problems I have to sort out.I just don't want to spend 2500 or so bucks on the top end to find that in a couple yrs the bottom end,or rings are going out!!
I need some advice here please!!!Funny,my handle really fits now huh??Thanks,MADRIVAGE

First off I don't know what a "running compression test" means. You cannot perform a compression test while the engine is running.
I would start over, and do a cold engine compression check on all cylinders and RECORD the results. If your paying the shop to do this, make sure they record the pressures of each cylinder for you.
If there is more than 10 % difference between any cylinders then do the test with engine Hot/Warm and record results.
Compare the two sets of readings.
If any cylinder jumps out as being "low", such as #3, I would then do a Cylinder leak down test of all cylinders and record the percent of leak down for each cylinder and record results.
If #3 or any cylinder has a high leak down rate, then it can be determined by the Tech whether it is a valve, Intake or exhaust, and/or a bad piston ring.
If you have never performed a leak down test, they apply air pressure directly into the cylinder and record the percentage of air leaking past any internal component.
For a street engine I've seen 10 to 15% leakage with a good running engine.
20% or more from a specific cylinder is an indication that it is worth looking at those cylinder(s) a little closer.

It is not "normal" for the 3800 to have these problems at only 125K miles. I wouldn't give up hope.
If you indeed have some losses from any particular cylinder, you may be able to bring it back into the normal range by cleaning the combustion chamber of carbon build-up with a good cleaning.
A machine/method that has worked for me is a Motor-Vac which will not only clean the combustion chamber but all of your fuel injection system including the fuel injectors.
A good Tech will also remove the Mass Air Flow sensor and perform a good cleaning of it along with the Throttle body.
Unless you have a very noticeable pressure drop in a cylinder, I have seen this service work to bring back cars that are running so bad you would have thought they were all done.
Motor-Vac is the name of the equipment sold by Snap-On and is used by shops all over the country. If you feel your engine is a candidate you seek out a shop that has the equipment and Trained Tech. It cost's me to have it done on our vehicles, every 30 -50K miles, about $200.00
If you do a search on here for Motor-Vac you should come up with a lot more info on this service and prices other people have paid.
I think my guy charges a little more than others, but he does take of the MAF and TB and cleans everything with the proper solvents using a toothbrush, etc.

I hope you don't have a cylinder going dead that can't be brought back to life. But even if it is determined that you have a bad valve and it is recommended that BOTH heads be done, you can be assured that the lower ends on these cars are good for 300K miles +.
I think the estimate of $2500 to 3000 is high, if a valve job is in order also.

So, I wouldn't freak out just yet. You have more test's to perform before condemning the cylinder heads or valves.

Good Luck and keep us posted as to what the compression numbers are per cylinder and the percent of leak-down on all cylinders.

After a quick read, and being a mechanic, my $.02.....

You have a Bank 1 Lean code, along with a misfire on Cyl #3 (which is Bank 1). Aside from the "compression" tests that were done, did anyone consider a leaky Fuel Injector to you?

Also, the LIM doesn't have to be leaking externally to be bad. They can go bad internally and cause a single cylinder issue and also the Bank 1 Lean code your getting. I suggest having a "better" mechanic look at it.....

As Rick has stated, no need to jump the gun and go right for the heads or cylinders.

Yeah, I would not freak out yet - - this is, however, probably the reason the PO sold/traded/dumped the car.

Aside to Rick: usually cylinder balance readings are sold to the uninitiated as 'running compression tests.' They are informative and easy to do but you are 100% right they are not a substitute for a compression check and certainly not a substitute for a good leakdown test.

Back to the problem.

One way you *really* WIN is that you have service records. Makes this easier.

YOu wrote:

"However,they noted that after a (running) compression test that cyl#3 was low which possibly indicated a bad valve or carbon build up...or a bad cam lobe. Where as a STATIC compression test showed all cylinders as healthy."

What I would do:

1) make sure all the spark plug wires are loomed propertly. crossed spark plug wires can induce misfires under certain conditions, and sometimes wires are bad/unsatisfactory new. The Rivieras have a very high energy ignition -- so high that it's kind of silly to put on the 'street racer' coil packs, they are no sparkyer than OE really. I am not there so I can not see your wires. What I've read on this board is that the OE wires are fine; Magnecor wires are better; Autolite, Bosch wires work gut not all that long. All that said, I'd guess the problem's not wires at the moment. But I would check to see that the wires are routed along the valve covers in the OE routing channels.

2) Cleaning the MAF and TB can only help and you really should. However since this misfire is only cylinder #3 I suspect it won't fix the problem. Again - no kidding you really should do it anyway. Put it this way - if after the car is warmed up you notice that the idle fluctuates enough to be visible on the tachometer (it "hunts" so to speak) then it is past time to clean your MAF and TB. Do a search on this site and you will find instructions for same.

3) Strongly consider getting a new injector and the needed o-rings, and swap out the #3 injector. The new o-rings are a MUST. O-rings get a "set" and if you disturb them, well if they have any age on them you need to replace them even if they were holding when first removed. If you don't invariably they will be the first to go--3 6 9 or 12 months down the road when you have forgotten why you pulled em in the first place... it would not surprise me if someone with more larceny than honesty in their heart swapped out the #3 on the PO because they needed one... clean cars are often targets of such petty activity - maybe Abaddon or another mechanic on here can commnet on what they 've seen in their careers workign in larger shops. Most mechs are honest, some are a piece of work...



4) THese cars do not have a 'history of eating valve' and I agree that on a well maintained vehicle this sounds more like an injector problem.

5) I kind of wonder if there is an issue with the ICM (it's the processor in the plate the coils are bolted to) but have nothing to base that on.

Summary: I'd swap out the #3 injector for a new one, with new o-rings. I'd pull the #3 coil (easy to do) just to look at it's attachment to the ICM (grounds?). I'd visually check wiring harness. I'd review service history and see if anybody ever might have flashed the PCM for some reason. I'd clean the MAF and TB. I'd consider pulling the valve cover to look at the valves to #3 (probably not a problem).

And I'd not worry too hard because again odds are this is a weird problem not a grave one.

After reading this will lthe rest of you with any ideas about this please comment?

Albertj

albertj wrote:

Aside to Rick: usually cylinder balance readings are sold to the uninitiated as 'running compression tests.' They are informative and easy to do but you are 100% right they are not a substitute for a compression check and certainly not a substitute for a good leakdown test.

So, just how do you obtain Cylinder Balance Readings that are used to determine a 'cylinder running test' ?
Excuse my ignorance, but I don't know how the health of a cylinder's compression can be tested other than performing a compression check and Cylinder Leak Down Test.
Is it done strictly with an electrical scope like what we used to use years ago and hook up to all the cylinder's ignition wires and see what the electrical firing resistance is.?

I've never heard of a "Running Compression Test". I've always done the Cylinder Balance and Cylinder Leak-Down test. Any other test is less than conclusive.....

If it were a coil/IC concern related to Cyl. #3, you would most definitely have a problem with Cyl. #6 also. This is not the case. Do an Injector Leak Down test to determine if the Injector is to blame. A leaky Injector would most definitely cause a rough idle/misfire concern, as the Injector would supply too much fuel, or not enough, which in turn would also cause a Bank 1 Lean/Rich code to match.

I would have also done a BG Fuel Injection/Induction service on this vehicle. Just in case of a sticky valve or dirty Injector concern, a good cleaning with the proper machine usually does the trick.

As far as taking parts off of a "good" car at the shop.....
If I ever saw another mechanic doing this, I would report him to my manager. If the manager failed to act, I would call the State and report him. Needless to say, I wouldn't be nice. I have NEVER seen this done btw.

A 'running' compression test is another name for a dynamic compression test. It is usually performed after a static test shows no problems with a cylinder. It's not something the average home mechanic can do, but shops can do it and locate problems more effectively. Sometimes they use specialized equipment to monitor the compression on an oscilloscope as the engine runs.

Basically, you take the plug out of the suspected cylinder, grounding the plug wire. Then attach your test equipment and start the engine. While running, the compression should read give you a reading at idle, and a reading under 'snap' acceleration. These two figures can tell you something about what's wrong with the cylinder.

Even if it seals fine under a static comp test, the cylinder may not breath correctly while running. During a running compression test, you compare inches of vacuum vs. PSI in the cylinder, considering the static compression ratio. If it reads low, it means air is not making it into the cylinder. If it reads high, it means air is not exiting the cylinder.

A cylinder that fails a running compression test indicates the problem is likely with the valves not opening or closing completely when they should. This would indicate a failed rocker arm, worn cam lobe, a bent push rod, or a sticking lifter. They should perform the test on more than one cylinder to be sure it's not some restriction in the exhaust or intake that's causing the anomaly.

However, unless the car was abused or not well maintained, I would not suspect anything is wrong with the valvetrain just yet. I might get a second opinion somewhere else. Don't tell them what you know, and see if they can isolate the problem to the valves using a compression test. I have never heard of this kind of problem on a 3800 engine. The valvetrain (along with the rest of the engine) is considered bulletproof.

If the LIM were leaking coolant into the cylinders, the spark plug would be dirty. It would show a build-up of deposits after only a few thousand miles, depending on the problem. Mine has been leaking slowly for many thousands of miles, and it has never caused a misfire or lean condition. I just change the plugs and oil more frequently until I can get the LIM gasket changed to fix the leak. If you want to know for sure you have a LIM leak, sent your oil to Blackstone for analysis. But if your plugs are clean, you have no reason to suspect it.

I think the lean reading is a clue. Maybe next step is to have your fuel pressure checked, try a strong dose of fuel injector cleaner in the gas tank. If that doesn't help, might replace #3 injector with a remanufactured unit (only about $30). If that helps, I'd replace all of the injectors, as they tend to become clogged by 150k miles. I noticed a big boost in power after I replaced mine.

I am not sure why you mentioned the supercharger at all, but it is not related to the problem, so don't worry about it. Our blowers are probably the most durable part of the engine, no joke.

Best of luck. I agree with the others that not all hope is lost. While it could be a problem with the valves, it likely isn't. Your static test rules out the piston and rings, so that's good. I would have a different shop check it out and see what they say.

AA wrote:

A 'running' compression test is another name for a dynamic compression test. It is usually performed after a static test shows no problems with a cylinder. It's not something the average home mechanic can do, but shops can do it and locate problems more effectively. Sometimes they use specialized equipment to monitor the compression on an oscilloscope as the engine runs.

Basically, you take the plug out of the suspected cylinder, grounding the plug wire. Then attach your test equipment and start the engine. While running, the compression should read give you a reading at idle, and a reading under 'snap' acceleration. These two figures can tell you something about what's wrong with the cylinder.

I would still like to know what this Mystery Test is and what equipment is used.
As I mentioned, years and years ago, we would hook up an oscilloscope to test various things (as that was the only major tool for testing engines)
One thing we could look at with this very large cabinet based tool with a huge umbilical cord of wires coming from it, was to hook to each cylinder's ignition wire and determine the health of the electrical part of the spark and could infer from that info that we had a bad cylinder. Pulling a spark plug and running the engine for the equipment is never done, as you have an open cylinder and would not be able to determine a thing.
Only during an actual compression test is a Spark Plug removed.
Have not seen a machine like that in 20 or more years as they are not necessary for diagnoses of the modern car, with on-board computers and such.
Plus, a skipping engine, even without OBD telling you that cylinder #3 is misfiring can be determined quite easily. If the health of the electronic side of the cylinder is determined OK, then you move on to the health of the internal cylinder itself, the air pump, and determine what's wrong with a comp test and/or a cylinder leakdown. As has already been discussed and is common knowledge.
I have worked in a GM dealership in the OBD2 age and we didn't have a Mystery Machine. So I am still confused on the terminology of 'Running Compression Test'. I personally have never used those words on a Work Order.

I would be interested in hearing from the younger guys who have been trained and worked more recently in the Dealership Service dept. or even the independent garage.

Rickw wrote:

I would still like to know what this Mystery Test and is and what equipment is used.
As I mentioned, years and years ago, we would hook up an oscilloscope to test various things (as that was the only major tool for testing engines)
One thing we could look at with this very large cabinet based tool with a huge umbilical cord of wires coming from it, was to hook to each cylinder's ignition wire and determine the health of the electrical part of the spark and could infer from that info that we had a bad cylinder. Pulling a spark plug and running the engine for the equipment is never done, as you have an open cylinder and would not be able to determine a thing.
Only during an actual compression test is a Spark Plug removed.
Have not seen a machine like that in 20 or more years as they are not necessary for diagnoses of the modern car, with on-board computers and such.
Plus, a skipping engine, even without OBD telling you that cylinder #3 is misfiring can be determined quite easily. If the health of the electronic side of the cylinder is determined OK, then you move on to the health of the internal cylinder itself, the air pump, and determine what's wrong with a comp test and/or a cylinder leakdown. As has already been discussed and is common knowledge.
I have worked in a GM dealership in the OBD2 age and we didn't have a Mystery Machine. So I am still confused on the terminology of 'Running Compression Test'. I personally have never used those words on a Work Order.

I would be interested in hearing from the younger guys who have been trained and worked more recently in the Dealership Service dept. or even the independent garage.

Running Compression Test

You need an oscilloscope to do this. If you put a mechanical gauge on there, it's not going to tell you much. Shops do this to diagnose valve train issues without needing to pull the valve covers to inspect.

RickW wrote:

Pulling a spark plug and running the engine for the equipment is never done, as you have an open cylinder and would not be able to determine a thing.
Only during an actual compression test is a Spark Plug removed.

A daynamic (running) compression test is and actual compression test, except he compression measurement is done with the engine running. The spark plug hole is plugged with your compression sensor; it's not such a far-fetched an idea.

More info on checking running compression: http://www.asashop.org/newsletters/mech/feb02mech.htm#6

You guys ROCK!!! I thank you for the quick and knowledgeable replies one and all.I am no stranger to spinning wrenches at all.I have built many a V8 in my muscle car days and diagnosed and remedied many issues with various "older tech" engines.But as you know the engines of today are a different animal altogether.An animal I am not as familiar with...not to mention the obvious,that I don't have a scanner in my toolbox YET.I have never heard of a running compression test either,I couldn't wrap my head around it.I have a compression guage which I had used in the past,and hve seen leakdown tests,but NEVER a "running" comp. test.So I gather this is an ":electrical pressure" test then??Anyhow,I dropped the car off at the mechanic this morn to do the struts and further diagnose the problem with #3 etc.He and his guy seem like very respectable dudes,not a lotta bullshit going on at all.I WILLL fix whatever the problem is with this car as I have fallen in love with it after only a week of owning it.It's such a great looking car,and it really rides nice and hauls ass!! I belong to another forum for a particular motorcycle that I bough a couple years ago,and they are a great bunch as well.I can see you guys are no different...I am VERY pleased to find that you guys are well versed in these cars,and not a bunch of snot nosed punks wih 30" rims and ill running cars.I hope to be of service to this board as I learn more about this car.I am a fast learner.I have mucho engine experience,just not with "newer" computer controlled cars...that being said,I WILL get a scanner/tuner set as soon as I finish up with this little issue and be "in the fold" so to speak. As a side note,I am probably going to go with a meth. injection system to address my KR issues and prep for a pulley drop in the future.So when all of the little bugs are worked out that will be my next project.I'll be sure to post a thread about it so we all can learn from it,as I have gathered from reading here nobody with a Riv on this site has actually bit the bullet and done it yet.I believe one of the "smart" systems with a control module and a super fine misting nozzle,coupled with a high pressure pump is the way to go as far as not damaging the impellers in the blower.I don't want to get into plumbing the thing in at the LIM for each cylinder.A little off topic I know,but there it is.Once again thanks,and I plan on sticking around and contributing in any way I can in the future. DON P.S. I'll pot again as soon as I hear form the shop in regards to the issue.

Thanks in advance for posting the resolution to this problem. All of us will be very interested in knowing what the issue turns out to be. Hope it's nothing more than a clogged fuel injector.

The 3800 is similar to the older V8s in many ways. The differences are mostly in the electronics, ignition system, and of course, fuel delivery. You will find that with scanning and tuning, although different than setting mechanical adjustments, are really much the same as with the older V8s. The difference is, you have a lot more control over things, because the engine management uses a feedback loop to make adjustments on its own. You set the desired target, the PCM will use sensors and make small adjustments in order to hit the desired target. It's an amazing system, and proven to work. It's good to see you are interested in learning to use it.

As for the water/meth injection, if you haven't found our thread on the subject, give it a read through, and post your experiences there. If I happen to find an affordable way to do it, I'm thinking about trying this as well.

Best, AA

Thinking about it, might also be a good idea to rule out the obvious and pull the lid off the airbox if you have not done so already. Just for kicks. See if there is anything in there not supposed to be.

FOr those of you who've read this far, here is an article by a Colorado vo-tech instructor on just this sort of problem on a 3800 engine, and the testing he did to find the issue. Turned out that in his case the #2 injector was not working. Measuring injector resistance did not help, all the injector coils measured 11-13 ohms like the book says. They ended up pulling the fuel rail with injectors connected and watching the injectors squirt.

http://www.asashop.org/autoinc/aug2004/techtotech.htm

For Rick, here is an article on the cylinder balance test. Some mechanics used to be taught that using this test one could infer that a cylinder was 'bad.' The misgivings that you shared, however, are all spot-on.

http://www.youfixcars.com/cylinder-balance-test.html

Happy reading

Albertj

Quote :

The misgivings that you shared, however, are all spot-on.

What comments are you referring to? Those regarding running compression tests?

A running compression test and a power balance test are two completely different things. Both are ways of determining a cylinder is bad, but the balance test cannot tell you why it is bad.

After reading the article on the 'Cylinder Balance Check' I have to say I have performed this test many times as part of a diagnosis of a rough running engine. Just never called it what it is.
It is a preliminary test that then allows the Technician to move forward with some of the other more conclusive tests.
Not necesarily done on every engine, especially if you already know you have a specific cylinder acting up.
At this point you will have done a compression check or a leak down test and not spent the time on the Balance Check.
Sometimes, however, if a compression test and leak down test do not show any problems then you can come back to the balance check. But with OBD2, the diag tool has already told you want you need to know, provided you have a good enough diagnostic tool.

What was totally confusing me was the inference that a plug was removed to do the Balance Test.
The cylinder is shorted out, a spark plug is not removed for the performance of the test.

I don't think it was inferred that you would remove a plug for a balance test. All you have to do is remove the ignition wire.

You do need to remove a plug for a running compression test.

Earlier in the thread there was reference made to 'cylinder balance' check, which may have thrown you off. The original poster mentioned a running compression test; this is a completely different thing.

AA wrote:

Quote :

The misgivings that you shared, however, are all spot-on.

What comments are you referring to? Those regarding running compression tests?

A running compression test and a power balance test are two completely different things. Both are ways of determining a cylinder is bad, but the balance test cannot tell you why it is bad.

We just had to post enough detail so we could understand each other w/r/t the various test names. "Disambiguation."

Albertj

Well kids the verdict is in.In regards to the lean condition in bank 1 code,it is a sluggish O2 sensor.As far as the MAF code it too is a minimally low voltage read,not much at all.Now,for the #3 misfire...the guy did a running check too,and said he compared it to all the other cylinders and it was ever so slightly lower than the rest indicating a valve issue.He said he was pretty sure it is a bit of carbon build up on the valve.He even went as far as running a smog test (for free mind you) just to see the outcome.As I already knew from the pre-buy smog test it passed with flying colors.He said it was a spotless run.In the end he just charged me $60 to test the O2 sensor,clean the MAF,and do the compression test.Not to mention he threw in my struts for $240 bucks.He was a very honest guy,and told me there was no reason to run out and replace my O2,or MAF as they were still more than adequate.As far as the carbon issue he recommended that I do a few heavy doses of (recommended)Chevron concentrated system cleaner) to see if it would clear up the carbon.The S.E.S. light s staying out for the moment.So,I would like to do one of these MotorVac treatments I have read about here,but when I looked p there website I couldn't find anybody in my neck of the woods doing it (just north of S.F.).On another note,while blasting down a rural highway in my freshly strutted Riv. with a tank of detergent to clean the valves...I got a F-ing speeding ticket!! LoL...whaddaya gonna do??