rough idle - 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 12-31-1969, 08:00 PM   #1
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Has any of you had a '92 (supercharged) with a rough idle and found out what caused it?

Mine has had a rough idle since I bought it in '99, and I've come across other '92 owners who have the same problem with theirs. Other than the rough idle, there don't appear to be any other symptoms.

My wife drives our '93 (supercharged) and it idles smoothly.

Thanks.
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Old 12-31-1969, 08:00 PM   #2
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Additional info: I removed the throttle body (and the IAC, TPS, and MAF sensors) and cleaned the throttle body. It was very dirty inside...unfortunately, it still has the rough idle.
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Old 12-31-1969, 08:00 PM   #3
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The negative terminal on the battery was disconnected while I did the work.

I didn't disconnect the positive terminal or do anything else.

Doesn't the engine "re-learn" its settings as it'* driven?
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Old 12-31-1969, 08:00 PM   #4
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Quote:
On 2002-02-05 10:26, billha wrote:
The negative terminal on the battery was disconnected while I did the work.

I didn't disconnect the positive terminal or do anything else.

Doesn't the engine "re-learn" its settings as it'* driven?
If you unscrewed the TPS from the throttle-body, than simply bolted it back on, you have most likely messed up the calibration. The TPS is a simple potentiometer that takes a 5V signal and varies the voltage based on how far you have it open. It must be adjusted to output a specific base voltage at idle or else the computer will throw error codes and may give you a rough idle, etc.

Here'* a great article on how TPS'* work: http://www.wellsmfgcorp.com/counterp...erpoint2_1.pdf

I can't remember the base voltage numbers off the top of my head, but I have it at home in my repair manual and will post it later tonight. I'll also post the pin layouts as well.
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Old 12-31-1969, 08:00 PM   #5
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The only way to "adjust" the TPS is to bend the arm on the back, and I haven't done that.
Actually it is adjusted by loosening the two screws holding it to the TB and then slide it back and forth...if you loosen them both a tiny bit you'll see what I mean, you can change the potentiometer setting by sliding it back and forth.
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Old 12-31-1969, 08:00 PM   #6
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Old 12-31-1969, 08:00 PM   #7
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.47V sounds about right, I doubt that is a big enough disparity to throw up any codes in the computer.

My experience with the TPS sounds similiar to yours. A couple months ago I removed the TB to clean it (my car has 140k on it and I figured it was due for it) and I mistakenly unscrewed the TPS, then put it right back on, not realising my error. I drove it like that for a couple weeks. My gas mileage went down the tubes (I was getting 15mpg) and the trans shifted very harshly (but it did go through all 4 gears - and the TCC did lock up). I also got the SES light every so often. I finally went out and bought a digital multimeter and adjusted it back and it'* been fine.

Did that fix your idling problem? How are your plugs and wires?
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Old 12-31-1969, 08:00 PM   #8
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I'm VERY frustrated...on what page and section of the shop manual did you find this information?

I have the 2-book '93 Bonneville set, *-9310-H-1 and *-9310-H-2, and I didn't find that info in mine. Information is hard to find because in my opinion the index is poor at best. My 1st book states that replacement of the TPS is simply to install it and replace the 2 screws. The 2nd book has the diagnostics for DTC code #21, and it states that the idle voltage should be between .2 and .74 volts, with no mention about adjustment or monitoring it with jumpers. I chose .47 volts just to be in the middle of the allowed range.

Granted, the throttle body and TPS I just worked on was on my '92 SSE supercharged, and the Pontiac shop manuals I have are for '93 models, but I also have a '93 SSEi and it appears to have the same TPS. The only difference I noticed was that its total TPS resistance was about 500 Ohms more than the one on the '92.

I'd be really curious to know if your manual has the CORRECT instructions for removing the water pump or the alternator (accessory bracket) for the supercharged version. The instructions in manual are wrong! And I have the Pontiac factory shop manuals!
Man! I wish I could offer you more advice, but my Bonneville is a 1992 SE and has a lot less things that can go wrong than your blown SSE (among other things, I lack an EGR valve).

Regarding the manual, the scans are from a Chiltons 1988-1993 H-Body repair manual, that I ordered from a Borders bookstore for around $20. It does cover the supercharged engine and I will see if I can scan in those pages for you.
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Old 12-31-1969, 08:00 PM   #9
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Alternator on VIN 1 (92-93 L67 engines)

<font size=-1>[ This Message was edited by: csprague on 2002-02-06 17:18 ]</font>
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Old 12-31-1969, 08:00 PM   #10
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Alternator instructions for 90-93 H-Bodies. I know these are correct because I've replaced my alternator before.

<font size=-1>[ This Message was edited by: csprague on 2002-02-06 17:38 ]</font>
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