Very Stumbling Idle 96 supercharged Riv

Hi guys once again.

I'll explain here alittle, this is my thrid new topic in as many days. I just bought this Riviera (96, 3.8 supercharged) and I am having some trouble so I have been leaning on the expertise of this board. For the help, i thank all who have posted, past and present. Last week I fixed a random misfire code (filthy injector).

Here is the latest issue, just started yesterday.

When driving, I notice abit of a stumble at idle, the RPMs would go up alittle (1000) and drop back down (750) in Park. It wasn't all that bad. Now the engine is still doing the same, but the RPM drops quite low to the point I think it is going to stall. I give it some gas and it hesitantly revs and sounds clearer. The engine speed dramatically drops and shakes.

I had it on a scanner last week and it was showing the Idle RPM to be off by 30-40. I have limited access to the scanner from work and I will try to get it this weekend. I have recorded all the information from last weekend, so I can refer back to it. I have cleaned the MAF, the IAC and the TPS. I shot some throttle body cleaner into the throttle body, not a great deal but it stalled the engine. The SES is not on, and the car shows no codes. I have ordered new AC Delco wire and plugs to put on this weekend.

Any advice or past experience to help me troublehoot this thing would be appreciated. I have ordered the FSM.

thanks,
Rod

my guess is - lack of maintenance. There are some high mileage/old age things to fix.

First - shooting throttle body cleaner into a dirty throttle body does not really help, in spite of what the lable says - you really have to pull and clean it. Get a throttle body cleaner that won't damage the special coating (find a CRC brand cleaner. In my area the NAPA, CarQuest and AutoZone have it). You will need to refer to the FSM to get instructions on pulling the throttle body if you have not doe so before.

Next problem, you'd need a scanner (NOT an OBD II scanner rather a comprehensive one like AutoTap; I use a PC application called Car Code with my PC and an OBD II dongle that attaches to the serial port on my laptop) to read the values of the various temperature and air sensors, and you also need some information (here is where the FSM comes in unless your scanner has the info already in it) that tells you what the values are supposed to be. Point is that you may have one or more sensors, including the oxygen sensors, that are just worn out. Or you may have an a wire to a sensor broken or poor connection. FOr instance, a loose connection to the oxygen sensor can make the idel hunt; fluctuating voltage from the alternator can do it too although it's usually viceversa (something makes the idle hunt and so the alternarot voltage varies with RPMs).

New wires and plugs may help but you really need to remove a plug or three to assess condition. Given the state of maintenance on your car I bet the rear bank of plugs is fouled bad bad bad (they are hard to reach and some mechanics don't change them but say they did).


BOttom line for me is you need to pull and clean the throttle body, use 'search' on this site to find the instructions. You also need an FSM and engine/drivetrain (not just code) scanner of your own.
Albertj

I agree with Albert on pulling the TB and cleaning it manually. You will be surprised how dirty it can be and wonder how the engine ran at all.
Also he's right on about the lazy mech not changing the rear spark plugs, it is a real possibility.

I don't see a signature with the amount of miles and year of car, so I can't comment much more than what has already been written. Just giving my $0.02 that's all.

Clean the whole intake or as much of it that you can get to. I'll assume you have checked the air filter and replaced if needed, the fuel filter should be replaced if you don't know when it was last done. If it has High Miles and you don't know history, I would either have a MotorVac done to clean your injectors and combustion chambers or remove all fuel injectors and send them out for cleaning and flow testing and balance checked.

Lot's of Preventive Maintenance items could be due or overdue.

If your not familiar with MotorVac, do a search on here and find a local garage that has the equipment to have it done if you feel it is due.

I would have said to clean the IAC valve, but you already did that, so yeah TB time.

IBx1 wrote:

I would have said to clean the IAC valve, but you already did that, so yeah TB time.

Another genius with no experience to speak of.

You all just post for the sake of posting and to repeat shit that you have heard other people say or have told you to do on your car. That's right, you don't even own a Riv, nor do you have the mechanical experience to be taken seriously.
Don't get in over your head. You may find yourself drowning in your own bull just like 97 Park Ave.

Oh yeah? Well I used to own a Riv and it did have a bad idle problem. I cleaned the IAC and that didn't fix it. The SES light was on and it was the crankshaft position sensor. Since his SES light isn't on, it's not the sensor. He's cleaned everything else out, so I'm reinforcing the possibility of the TB screen being clogged.

Taking your meds tonight?

IBx1 wrote:

Since his SES light isn't on, it's not the sensor.

THAT right there helps to prove Ricks statement....

Abaddon wrote:

IBx1 wrote:

Since his SES light isn't on, it's not the sensor.

THAT right there helps to prove Ricks statement....

Ya...

Hey guys can we lock the riffraff stuff to somewhere else and help the OP with his problem here?

You may also have to clean your MAF sensor and you may have dirty or leaking injectors.

nothincame2mind wrote:

Abaddon wrote:

IBx1 wrote:

Since his SES light isn't on, it's not the sensor.

THAT right there helps to prove Ricks statement....

Ya...

When my Riv had its first stumble, the light came on. If his car has been doing this for a while, then his SES light could be broken, who knows.

ibx1 wrote :"then his SES light could be broken"

you can be sure that the most reliable component that GM has ever produced is the SES light.

robotennis61 wrote:

ibx1 wrote :"then his SES light could be broken"

you can be sure that the most reliable component that GM has ever produced is the SES light.

Haha, don't I know it!


Any progress with the car, Rod?

IBx1 wrote:

Oh yeah? Well I used to own a Riv and it did have a bad idle problem. I cleaned the IAC and that didn't fix it. The SES light was on and it was the crankshaft position sensor. Since his SES light isn't on, it's not the sensor. He's cleaned everything else out, so I'm reinforcing the possibility of the TB screen being clogged.

Taking your meds tonight?

Well Genius,
Not that it's any of your business but I am on med's all the time.

And, I had a similar problem as the OP, No SES light and it turned out that after doing all the other things already mentioned and recommended, good PM by the way, the replacement of the CPS did solve the problem.

At this point in the troubleshooting process I deliberately did not mention that because all the other things mentioned need to be done first to rule out dirty and inoperative fuel and induction components. If after all those items are taken care of and the problem persists then I would suggest looking at the CPS but not before.

By bringing it up prematurely you can offer confusion to someone not familiar with this engine.

And the Crank Position Sensor can and does fail without tripping an SES light. So, once again, unless you really feel qualified to troubleshoot someones problems, I would stand in the background and listen.

deekster_caddy wrote:

You may also have to clean your MAF sensor and you may have dirty or leaking injectors.

Derek,
Just so you know, the OP's first post states that he cleaned the MAF as well as other things and the recommendation to clean the injectors was mentioned in a previous post as well.
If we left Ilan to troubleshoot this guys car, he would have him change the Crank Position Sensor before the logical approach was taken and all the other Preventive Maintenance items were taken care of first. That was my point and my only point.
A new guy will have no idea what kind of experience he has and may just replace an expensive sensor for nothing.
Rick

HI GUYS IM HERE FOR THE GANG BANG?!?!?!?!?!

just a comment from the sidelines:

1) I've gone thru 2 crank position sensors (CPS). The first - the original - failed such that the car would start and it idled just fine, but what would happen is you'd shut the car off and then it would not restart unless/until the engine was pretty much cool enough to touch. The dealer could not diagnose the failure because of how the powertrain control (PCM, generically the ECU) uses the CPS in the startup sequence. When the CPS fails it kind of looks to the PCM that the key was turned off. Hence the PCM does not turn on the check engine or service engine light (no MIL). The second failed such that the car would quit while running - still no MIL - but a known problem to the dealer service department (they change it the first time and used a Standard) who replaced it again but *this time* with a Delphi. POINT IS Rodman's car is running but not running well, and the idle problem is there whether cold or hot. The failure that I am seeing here does not match any CPS failure pattern I have seen in the past, so I am not even thinking about the CPS in Rodman's car being a problem. All that said, it would not be a waste of time to check the *wiring* to the CPS, in case the real problem is a mouse or some such has chewed into the wires or that road debris or prior maintenance damaged them. The thing about the CPS is that its behind the harmonic balancer (HB). You really need the HB puller (you can make one up with a standard one and different bolts, there is a writeup on that) to get it off/on without breaking the rubber part. To get the CPS off you need to jack the car up and pull the passenger side front wheel, the fender liner, then the HB. Second point is if you were thinking "it's only a $50 sensor lets swap it and see what happens) you were, well, mistaken. Unless, that is, you like pulling the HB.

2) I have noticed that many people who buy Rivs with relatively high miles, relatively low price usually under $1000, do not necessarily budget the time and money needed to assure themselves the car gets to the level of maintenance needed for reliable operation, and often find that the previous owner has left them with a lot of deferred maintenance. Some of them are game to learn how to make the car work and some will hate the day they bought in. The learners will ask a lot of questions, and that's OK - we either answer them or point them to the writeups. Those who hate the day and don't want to learn how to work on it themselves usually just vanish after the mechanic bills turn out to be more than they paid for the car. Don't get me wrong, it's usually for good reason they have not allocated the budget needed to run a luxury car, but they just did not factor maintenance into the buying decision. So once they have the car, if the low city MPG does not freak them out the high repair bills will. Even if the car is right and tight when they buy it, they are not ready to spend the $200 - $300 on a monthly basis for just the maintenance to keep it running. I understand that issue. If there is any good news here it is that once you get the problems straightened out the Riv is pretty reliable and not a maintenance nightmare. The trick is that if you are going to use it as a daily driver then you need to (1) figure on spending a couple or three grand a year to keep it on the road (2) learn to do as much maintenance as you can yourself so you *don't'* spend that 3 grand (3) recognize that if you have a collision you most likely are out of the car - or at least, you settle with the insurance company for less than the cost to repair it, and "salvage" it.

3) One of the problems with drivability problems (not just on the Riv) that *don't* turn on an SES light is there's no code to point you in any direction. When cars did not have SES lights, trade schools taught a lot more about how to troubleshoot cars. And mechanics had to know how to do that. Nowadays a lot of what seems to be happening is that those of us who learned how to troubleshoot cars prior to the advent of SES lights - or at least, learned to troubleshoot on a pre-OBD car - get lots of chances to share wisdom and insights with those who learned later or whom have not had the chance/need to learn it at all. Worse, the mechanics sometimes find that old-school troubleshooting, well, puzzling at best.

4) About the throttle body (TB) -- if it is not gummed up too bad you probably won't need a new gasket to put it back on. But no kidding you have to pull it to clean it because when you just spray cleaner into it, you don't clean about 35-45% of the surfaces - nothing behind the throttle plates really gets clean. When those areas are not clean, the sensors in proximity such as the MAF by and large don't read true. The first hint that you need to pull the throttle body and clean it is that the idle will "hunt" that is, it will waver up and down by 100-200 RPM or so. When the Riv is running right, you should be able to have the engine idling and the tach needle should not really even quiver. If the motor mounts and such are right and tight, you may not even be able to hear the engine at idle if you're sitting parked on a busy street with the hood and doors closed, and windows up, in a Riv with stock trim and exhaust. Now about the OP's problem - by the time a Riv starts to do the big hunting at idle, there's been a lot of maintenance that's just been blown off. Fortunately, most of it is labor time and not that tough. So a problem that would cost you over $150 for a mechanic to do, like replace the plugs, will easily run less than 1/2 that and usually much less if you do it yourself. Trick is to find and fix all the stuff before the car strands you in West Gybyppe some cold rainy night.

5) There is a remote chance the PO or a mechanic removed the SES light. In practice this rarely happens, especially on the Riv -- it's really tough to get to, you have to pull the dash panel and then the instrument cluster because most folks can't reach that part of the cluster from under the instrument panel. This is why you read the codes anyway - find the stored codes and such. This is also why you want your own scanner, not only to read and reset codes but also to read the values from the sensors so you can more easily spot stuff that is out of whack.

6) it wouldn't be a waste of time to check the wire harness and plugs, the huge ones, at the fire wall and at the coil pack.

So - you have your work cut out for you so to speak, but keep at it and you'll get it right.

Albertj

Hey guys,

Thanks for the leads here. I could not get ahold of a scanner for this weekend. I just placed an order for an AutoTap, will be in wednesday

I am just going to rip off the Tb and give it a good cleaning. I got the gasket today. Saturday I will put plugs and wires on. i'll keep you updated.

The SES light does work,as I fixed the random misfire code. I don't really know what to think of this situation as has just come out of know where. But I don't think previous owners did much in terms of maintance.

i'll go throught the troubleshoting steps and keep you guys posted.

Thanks again for the help
Rod

Good Luck and let us know how it turns out or if you have any questions.
Rick

Well Rod, you just answered the big question: The SES light does work... And you've also covered most of the obvious possible problems.

Unfortunately, from reading here for a couple years, the main thing that seems to screw up these motors without throwing a code IS in fact the crank sensor... However, it sounds like you can probably get your hands on an HB-puller if new plugs, etc. don't fix it.

And for my own 2 bits, I think if you had an ignition problem, idle would be the least of your problems - Under load would be the big deal.

Eldo wrote:

Well Rod, you just answered the big question: The SES light does work... And you've also covered most of the obvious possible problems.

Unfortunately, from reading here for a couple years, the main thing that seems to screw up these motors without throwing a code IS in fact the crank sensor... However, it sounds like you can probably get your hands on an HB-puller if new plugs, etc. don't fix it.

And for my own 2 bits, I think if you had an ignition problem, idle would be the least of your problems - Under load would be the big deal.

That is one thing that bugs me - the crank sensor. I admit it could be flaky but I've never seen em cause this patter of problem. With a scanner though the crank sensor output can be read and if it's flaky it'll be apparent. Like I'd mentioned before I for sure would be checking the wiring to that sensor.

Albertj

albertj wrote:

That is one thing that bugs me - the crank sensor. I admit it could be flaky but I've never seen em cause this patter of problem. With a scanner though the crank sensor output can be read and if it's flaky it'll be apparent. Like I'd mentioned before I for sure would be checking the wiring to that sensor.

Albertj

Albert, I agree with making sure all the wiring is good FIRST and there are no breaks or even partially frayed wiring from PCU through the firewall and through the engine compartment to the sensor's, but after looking at and cleaning many things on my engine and looking again with a Snap-On diagnostic tool that was capable of data steaming and more, we stumbled on the slightly erratic behavior of the CPS and because we had looked at and tested wires and connections everywhere, I bought a sensor from NAPA and replaced mine and the problem went away. I have subsequently bought one from GM to have as a spare when the NAPA one takes a dump.
But I didn't shotgun this replacement either.
Went through many hours of diag and cleaning and testing, because I had no SES light and finally watched the CPS closely and thought we saw something that was worth the expense of changing the sensor and Remember Everyone - Do a Crank Re-Learn procedure before replacing the unit, re-test and verify then replace the sensor and perform another Re-Learn Procedure.
My idle seeking went away.Yet this could have been just a dirty sensor pick-up, dirty or weak connections at the CPS,etc. You just never know once you start messing with stuff that is relatively delicate, yet robust enough to live in that environment.

albertj wrote:

That is one thing that bugs me - the crank sensor. I admit it could be flaky but I've never seen em cause this pattern of problem. With a scanner though, the crank sensor output can be read and if it's flaky it'll be apparent. Like I'd mentioned before, I for sure would be checking the wiring to that sensor.

Albertj

I had a similar thought, but if it was one of the 'classic' broken wires, wouldn't it also be very intermittent?

Eldo wrote:

I had a similar thought, but if it was one of the 'classic' broken wires, wouldn't it also be very intermittent?

Well that depends on a lot of potential variables, don't you think.

Rickw wrote:

Eldo wrote:

I had a similar thought, but if it was one of the 'classic' broken wires, wouldn't it also be very intermittent?

Well that depends on a lot of potential variables, don't you think.

Voltage variables ARE 'potential' variables...

Touche'
If I were going to use the terms interchangeably I would have said so.

Just so everybody else knows the word Potential is used in electrical vocabulary to mean Voltage.

Wasn't quite what I was trying to get at but, I'm done now. Toast.

I knew you'd get it...


(BTW, if you go back to Page 9 in the LIM thread, you'll see I answered your "devil's advocate" question at length.)