unstable engine - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 10-18-2003, 09:56 PM   #1
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I have a 92 se it has a rough idle in park but gets worse when i put it in gear. when i come to a stop the whole car shakes a lot. when i step on the gas it feels like it wants to stall out. it has no power. there are no engine mods. i have replaced the fuel pump/filter, coil pack, plugs, wires, harmonic balancer,and the ecm all due to unrelated probloms. the car did run the same before i replaced this all. please help i am desperate.
thanks!!
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Old 10-19-2003, 08:26 AM   #2
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maybe it has a burnt valve? its one of the 92'*.. like MINE! lol.. can someone help me out here on this?



Rob
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Old 10-19-2003, 09:50 AM   #3
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Well, if you had mentioned it had set off a code, I would say start there, but assuming it hasnt, I would be inclined to check cylinder compression, it could be a bad valve or something other. But a compression check will be able to tell you that. I would also suspect the timing, ie. timing chain, cam condition, or possibly coil pack going bad. It is a process of elimination. Have you checked anyting like this yet?
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Old 10-19-2003, 12:25 PM   #4
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the coil is brand new. i haven't checked the timing or the cylinder compression though. i think that i will do that this week and let you know how it went. thanks for your help.
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Old 10-19-2003, 03:49 PM   #5
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A Bad Valve will NOT EFFECT IDLE though. A Bad Injector will! A bad valve will give you a slight of "miss" & a "ticking" noise. A bad Injector will cause over or under fueling. How'* your TPS? Are the mounting bolts tight? How about the MAF? When was the last time the TB was cleaned? How about the IAC Motor, was it cleaned recently? All these things WILL EFFECT IDLE!
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Old 10-19-2003, 04:58 PM   #6
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I cant say I'd totallt agree with you DEATHRAT, a TPS or MAF if signaling out of it'* voltage preference would set off a code, especially if the ECM couldnt compensate for it. A valve that is burnt or has a buildup on it will not seat properly, thus eliminating the cylinder coming up to pressure (exhaust would do it) and would create a loss of power, poor idle, and horrible performance especially under a load, and may not tick, (a really bad timing chain would do this too). I would agree, however that another possibility would be to check the injectors. But that will still fall under the process of elimination to try and eliminate what it ISNT. To find the culprit cylinder (or cylinders) the plug wires can be pulled "one at a time" while the engine is running (with insulated pliars -made for this) to see which one "does not" effect the rough idle. (a good cylinder, when pulled- will make it idle even worse) This, at least - will signal which cylinder (or cylinders) is not performing properly. Then the troubleshooting process can be narrowed to where the problem is. Just be careful when pulling plug wires while the car is running, plug wires will "BITE", and you have pulleys that would take you in a heartbeat. I have went through before hand and pulled them first, and gently put them back on so they wont be a struggle trying to "pop" them loose while your under the hood.
Good Luck
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Old 10-19-2003, 06:00 PM   #7
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Jkinney, for the sake of argument, I'll have to go with the Rat on this one. I've seen TPS and MAF failures that didn't set a code or SES. And this does sound very much like a bad injector or dirty TB, assuming the ignition components are in pristine condition.

I pulled my TB off at 70,000 miles, and it was disgusting. anyone with this type of problem should consider cleaning the TB if it'* been awhile.
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Old 10-19-2003, 06:31 PM   #8
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two weeks ago i did have the intake off of the engine to replace the gasket durring this i cleaned the tb verry well. i put new o rings on the injectors as well. i thought about the tps but havnt done any thing with it yet.
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Old 10-19-2003, 08:51 PM   #9
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projectbonnie,
this souinds like exactly what happened to my bonny a few months ago. after the popel at midas weldedin my new muffler they had freid one of my coil packs since they didnt disconnect the ground battery cable. when i started it up, it had a very horrible idle, and the first thing tthe guy asked me was if the idle was this bad when i brougt it in. of couse i said f**k no! then i drove it around the parking lot punching it and testing the performance. and the car would shake violently from the missfiring.

so basically i would check to see that your ignition system is working, coils and the modual underneath it that controls it (c3i modual for me)

hope this helps
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Old 10-19-2003, 10:01 PM   #10
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Willwren. I wouldnt argue that Rat doesnt have a good case, looking back at the recent posts, I would have to say there are good suggestions, thus far. I just disagreed with him saying a bad valve would "NOT AFFECT IDLE", ( not arguing ) . I simply suggest that I would eliminate anything mechanical aside from checking the normal "visuals", loose sensors, leaking injectors, shorting plug wires, vacuum hoses, no codes etc. I would hope that everyone would do a thorough look-over before diagnosing. We are all just guessing based on what projectbonnie knows, thus far. Some of these symptoms can be characteristic, but not all problems are common. I suggest that he try and isolate the problem area, and then eliminate if there is fuel, and fire. Isolating the cylinders one at a time is still a good process of doing this. The ECM monitors everything except secondary ignition, fuel, and mechanical condition engine components. If there wasnt a code set yet, I wouldnt consider that until I have checked the other possibilities, I personally dont like getting out the digital volt meter and pigtails, until I have to, ....some can be a real pain to get at. I'd have to think his ECM is working properly since it is new (but cant guarantee it) I hope for his sake it'* an easy fix.
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