Idle Problem in Drive Only - Stumbles, Shakes

Well, other than the speeding ticket all went well.
As far as Motor-Vac sites, I found the list to be not complete. The guy down the street from me has one and is not on the list.
I guess it's up to the individual who buys the equipment to put themselves on the list and a lot of them don't even know the list exists.
So, you may want to call around to different shops and if you have no luck the next best thing would be a BG Treatment although after having seen both treatments being accomplished on a vehicle and understanding how they work, I would search for the Motor-Vac as far as getting your combustion chambers and fuel injectors the cleanest. Putting additive in your tank most likely won't solve this issue. After a thorogh cleaning then you can maintain by putting in additive's if you wish.
These cars in general were driven by people that did not go WOT and the carbon builds up. The atypical older crowd bought the car and just drove it easy. Now it's time to clear it out without killing it. If you know what i mean.
Good Luck,
Rick

p.s. I too had a lazy O2 sensor that was tripping my SES light occasionally and I finally replaced it to eliminate the annoying light as it became more frequent.
The thing with the light is, if you don't have the equipment to read what is causing it, you could be thinking it is Just the O2 and not worrying about it, when it could be something else worthy of your attention.

I'd go for the BG Fuel/Induction service myself. I do it once a year to keep it clean. There is no fuel tank additive that will clean as well or as fast as a BG Treatment done properly. If you are not familiar with it, I'll explain.

First, we take out the Fuel Pump relay to disable fuel. Hook up the "machine" to the Schrader valve on the fuel rail. With the machine pressurized to around 35psi, we start the car. The car then runs on only the cleaner, through the Injectors, until it's pumped dry. I reinstall the relay. Now I disconnect the air intake tube at the throttle body and insert a little sprayer (set to about 80psi, which vaporizes the liquid) as close to the throttle plate as possible. I start the car and open the valve on the machine (we are now using an upper intake cleaner). I hold the throttle plate open so that the cleaner makes it through easily. This part of the process is when I see (and smell) the most benefit. The exhaust gas turns dark and stinks to high hell, which means all that built up crap is blowin out the tail pipe. This cleans the throttle body, upper and lower intake, valves, etc. After the tank is dry, I put everything back together and then dump a Fuel System treatment into the Fuel tank. After all this, I go for a test drive with at least 1 WOT run to clear out any remaining cleaner that may be pooled up somewhere in the intake. It's a very beneficial 3-step process as long as the tech doing it takes care to do it right. I've cured many lean conditions and minor misfire concerns with this treatment. It costs around $120 to do. This includes parts and labor.

Sorry about the whole explanation, but I'm sitting here at work waiting for parts on 3 cars!!!

moldymac wrote:

How do you guys feel about running some seafoam through the engine? It is suppose to break down carbon build up. I have run it through my engines in the past, and if not anything else, the idle on my Chevy truck was a bit smoother afterward. Might be worth a shot, under $10 and its easy to do.

I use Techron in the tank about every other oil change. Hint: do it on the high end of the permissible concentration - read the label for details - and put it in when tank is 1/4 or *less* full so it mixes right then add gasoline quantity sufficient to meet the label specs.

I used Seafoam once. It was fun for the first minute and a half having the plume of smoke coming out the tailpipes. But it got old quick. madrivage, suggest you consider cleaning the TB by hand if only to keep stuff like Techron or Seafoam from merely moving the deposits downstream. BG and Motorvac do a better job on the parts you *can't* reach easily, but pulling the TB is not that big a deal - there are instructions on this site if you need 'em.

Oh by the way about that O2 sensor - if you go ahead and replace it your gas mileage will probably go up but depending on how much you drive not necessarily enough to break even for a while so to speak. The winning move is to shop around for it, maybe get it from RockAuto.com and install it yourself, they usually have 'em not much $$. For instance the Denso that fits exactly (they call it OE Style) is $35, not much more than the universal and way better, my experience (with other cars) is that even if you put another 100,000+ miles on the car you will not likely need another O2 sensor if you put in the Denso.

While we're on the subject - I'm not sure how long the downstream sensor lasts in a Riv that is well maintained, my scanner says my downstream sensor is still fine almost like new after 100,000+ (it was a OE from GMPartsDIrect). My experience is the upstream ones are weaker at that mileage. The dealer can flash the PCM with programming to compensate for the weaker sensor, but at this point I'm not sure how many of them have techs who remember how, or who would check the TSBs if you brought it in for say a state inspection or some such.

Albertj

This was the #6 wire...it was chewed by rats,AND melted to the damn core!!The #4 was corroded at the coil side terminal to boot.I guess it was a good time to swap wires and plugs (605's). I haven't taken her for a spin yet,but I am about to in a minute.I'm sure she'll run better after swapping from stock plugs which all looked good btw,(no problems with LIM at 125k miles).Ditching those bunk wires for new stockers should also be an improvement.I'm surprised it wasn't missing horribly with that chewed up wire.

what is it with rats and wires? whats the attraction? are they just excersing their right to chew? good thing you caught that ..

I think it will run much better now.

Wait till he try's it out.!!!!

Well,it's pulling a lot harder now and,damn near all of the ping is gone.I would mash the throttle before,and when under any sort of load I'd get a light but noticeable ping for a brief moment and the kr would kick in.Now I floored it under load a few times with no ping at all,then the last time I floored it I heard the faintest ping as it was about to shift into 2nd.I suspect I got it a little warm by the time I floored it the last time,therefore it whispered a little ping.All in all not as horrible a job as I thought it would be other than shredding my left arm.The only bummer is I STILL have that little stumble at idle when in drive while stopped at a light etc.I have cleaned the MAF twice,cleaned the idle air valve,and now replaced the plugs and wires.Not to mention I've Seafoamed it multiple times (via intake and in gas tank) to no avail.I think it's related to my low comp. in #3 that is supposedly due to carbon build up( I mentioned it in a prior post).I am having a hard time finding a Motorvac service nearby...I hope that will take care of my problem.Otherwise the car runs like a bat outta hell.That coupled with a low "running" comp. in #3 and normal static comp. test leads me to believe it is a carbon build up issue.It seems to have gotten a little better with my constant fuel system douching,but its still there.The Chevron concentrated system cleaner seems to have worked the best as far as cleaning up the idle is concerned. Don

Seems like the car was severely neglected by the previous owner. There could be multitude of things contributing to the stumble from a stop. If you've already done the Seafoam treatment more than once, I'm not sure the Motorvac is the best use of funds. The way I understand, it's very similar to Seafoam.

If it were my car, I'd send an oil sample to Blackstone labs. It's only about $25 - they provide a very informative analysis and are knowledgeable of 3800 engines. Might be the clue you need to better understand what's happening inside the engine. See thread:

https://rivperformance.editboard.com/care-maintenance-f8/mostly-good-oil-report-analysis-blackstone-labs-t2572.htm

I might just do that (send in a sample).The stumble is not a stumble off idle when accelerating,it is more of a little miss like kind of stumble during idle itself.If I hit the gas from a stop or from a roll for that matter there is never any sort of stumble...the car runs excellent and has gobs of torque,and snappy acceleration.I just haven't been able to chase down this slightly rough idle situation.

Yes, I've found on my previous cars that the Techron/Techroline is expensive, but very good. Carbon in #3 might explain the pinging, too... the carbon makes hot spots, and maybe with it only in one cylinder, that is the reason that you're even getting audible ping.

I've done a lot of WOT running with the scanner connected, and I've never heard a ping even when I know that knock retard is engaged. The sensors can always hear it before I can (and I have very acute hearing - no rock concerts

For now, I'd keep dosing the tank with Techron and see if it will eat away the crud.

Have you checked for a vacuum leak? I would cause the idle problem, while running fine otherwise.

I wonder if you were hearing ping before, or a misfire. Often when an ignition wire goes bad, the result is a stutter or pulsation under acceleration. It could be confused as knock. I've heard both sounds before. If you want to hear ping, fill with 87 octane and find a hill to drive up...

Has the misfire code on #3 returned since you replaced the wires? Since #3 and #6 fire from the same coil pack (waste spark), that likely explains the misfire you reported. I would almost think that problem is solved unless I saw the code again.

AA wrote:

Have you checked for a vacuum leak? I would cause the idle problem, while running fine otherwise.

Well now you're just being a sensible SOB!!

I can't believe I overlooked that...

Well as far as hearing ping before...it def. was a ping and not a misfire.We only have 91 octane here,I dunno if that makes that huge of a difference or not.I am a musician for longer than I'd care to admit and my hearing is pretty ridiculous...so when I say faint I mean it,but it was there.There was never any shudder or pulse such as would be felt from a shorted wire or misfire...I've felt that before.The acceleration and anywhere else in the r.p.m.'s feel great...it's just the slightly rough idle when stopped at a light in drive I can feel it.It's a little stumble/miss that can be felt through the steering wheel.I'm assuming it's due to the issue in #3.I just don't get how it can run so great and not feel unbalanced or rough and have this little miss/hiccup.I am very tuned into my machines and have built a few engines myself,so I can feel everything and the engine is in otherwise perfect health as far as I can tell.

Considering you cad a completely chewed and eaten ignition wire and i know from my experience and others on here that an even slightly cracked vacuum hose can cause issues that you wouldn't expect.
I don't why for sure or if it's because this is my first supercharged engine, but i would have sworn had a much bigger problem with my car before i went a bought some different diameter lentgh's of fresh vacuum hose and replaced everyone under hood.
It absolutely made an instant difference in my idle vibration /hesitation issue and all for less then $10.00 and some dirty time under the hood.

If you haven't already replaced all of them, it certainly is worth doing regardless of the outcome.

Rick

Hey AA,I looked for a vacuum leak,it was my first thought too on an otherwise great running engine.It was ALWAYS a vacuum leak on the older cars I was working on that caused a shitty idle.Unless there is somewhere unique to this car that is prone to a vacuum leak that I don't know about.I suppose I could pick up a can of quick start and spray around some?One thing that keeps popping up in my head is the LIM.I'm pretty sure it's the O.G. set in there,they look like black plastic to me on the visible edge that I can see.So could there be a vacuum or pressure loss in an intake runner say for #3 that could cause the little rough idle and the low comp. in #3 during a run test and not a static comp.check?My oil/antifreeze are spotless,I burn no oil whatsoever,and there is no blow by...not to mention the plugs I took out today (stock irridium with approx40k on 'em) looked PERFECT.A nice tan with no glazing or spots whatsoever.

So Rick are you saying you replaced all of those little plastic vacuum lines,or did you just replace the rubber ends?Or are you talking about a whole other set of lines that I can't see?Damn,you might be onto something though...that fucking rat ate my spark plug wires...why not a nummy-nummy vacuum line for desert??so can you clear up for me if there are any hidden lines other than the hard plastic ones I should check out?? Thanks man.

madrivage wrote:

So Rick... you might be onto something though...that fucking rat ate my spark plug wires...why not a nummy-nummy vacuum line for desert??

Precisely! However, there is no mystery to these cars (unlike, say, a Ford)... If you have already looked for a vacuum leak, you probably have not missed anything. With everything that has converted to electrical, the only vacuum lines left are the brake booster, the supercharger controls, and the EVAP system...

madrivage wrote:

So Rick are you saying you replaced all of those little plastic vacuum lines,or did you just replace the rubber ends?Or are you talking about a whole other set of lines that I can't see?Damn,you might be onto something though...that fucking rat ate my spark plug wires...why not a nummy-nummy vacuum line for desert??so can you clear up for me if there are any hidden lines other than the hard plastic ones I should check out?? Thanks man.

No I replaced all the rubber lines and found even though they looked good once I started messing with them they started cracking and showed their age quickly.
It's just worth doing at the age and mileage of the car.
Also, while your doing that, it gives you the chance to really look closely at all the plastic lines that wrap around the engine to the back. Some area's require a mirror to inspect them closely and you could easily have a plastic line that has been chewed on as well.
The other things to look at closely are the factory reducers that attach to the plastic and rubber lines and other things. They can fail and be hard to see until you look closely. They are hard to come by and you can get creative if necessary with various things from the auto parts store or a donor car with good plastic and fittings.
Or I think they can still be ordered new from GM.

Just saying that in the process of replacing the few rubber pieces that are on there you get the opportunity to look at all the other stuff, visible or hidden much more closely.

I had an occasional (somewhat frequent) stumble at idle until I had my injectors cleaned, externally on a flow bench. I haven't had experience with the motorvac or other on-car treatments but they sound reasonable to me. Truly dirty injectors will cause that kind of occasional stumble at idle.

Didn't (we) mention Injectors on Page 1? You still need to do a fuel pressure leak down test.........A leaky injector will cause EXACTLY what your are still describing.

Great that you found all those chewed wires, but the "real" problem still exists......

Scott is right. It's mentioned earlier. I have been partially following this thread and didn't realize it had already been covered. Anyway, it's time to have a good cleaning done on your injectors, and a thorough injector test.

If you don't want the downtime of sending your injector's out, then first clean around them, replace the O-Rings (available through your parts store cheap) get Fel-Pro's and find a competent tech with a Motor-Vac and you'll be surprised at the results. I know I was the first time I had it done on another vehicle i owned.

That is after doing a bleed down check, but I can almost guarantee that with your miles you will feel a difference, if not solve the issue.

p.s. I would still do all the vacuum lines and a thorough inspection of the plastic lines as mentioned before. Just good preventive maintenance.

Same thing with planning the LIM gasket change as I am doing for PM. I don't want to wait for the inevitable to happen.

Quick update.I dropped off the car (at dealer...I know...) to replace the rear transmission mount...it was shot.I asked him if they had a Motorvac unit,and they do not.However,they do have a Wynn (sp.) machine which works on the same principle.He said they pull the f. pump relay and tap into the fuel rails and run the chemical through until it's gone,then clean the throttle body,and finish off with a tank treatment dose.I am keeping my fingers crossed that this will clear up any slightly rough idle,slight ping at W.O.T.,AND the supposed carbon build up in #3,which may be the cause of all of the aforementioned probs.

Hope the treatment doesn't cost too much, and hope it works.

But, I still have to ask... have you seen any more misfire codes since you replaced the #6 plug wire? Imo, that wire was causing the miss on #3.

sorry...no I haven't seen my Check engine light for a few days now,it would only pop up after a day or so driving,then go away.I don't have a scanner though.As far as #3 cyl. I am more concerned with the verified low compression during a running test.That is why I went for the system clean...to hopefully rid me of any possible carbon build up that might be causing the lower comp.