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.

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.

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.

Thanks for the TPS link, but I don't see how removing and reinstalling the TPS affected its calibration. The metal arm on the back of the sensor rides on a rotating pin which is rotated as the throttle is opened. The only way to "adjust" the TPS is to bend the arm on the back, and I haven't done that.

The engine runs as it did before - steady RPMs at idle, but the idle is rough. There'* no stalling, sluggishness, poor fuel economy, "flat spots" in the throttle response, or any other symptoms as far as I can tell.

-Bill

Come to think of it, I do remember seeing the ovular mounting holes but I reinstalled the 2 screws so they contacted the same points as they did before I removed them.

The engine idles steadily at around 750 RPMs.

If you have any info about a calibration procedure, I'd appreciate it. I also wonder if I should look at the idle adjustment screw on the throttle body - I've never given any thought to adjusting it.

Thanks.

You were right csprague - the SES light came on momentarily while I was driving on the freeway last night. It wasn't even on long enough to cause the bell to chime, but I checked the error codes and #21 was present (TPS high error).

It may have been due to the combination of the TPS position being slightly misadjusted and the fact that I turned on performance shift for a while yesterday - oddly enough, that was the 1st time I've used performance shift since I've had this car!

The 1993 Pontiac shop manual said that if this DTC code is set, the tranny won't shift into 4th gear and the TCC won't lockup. But that'* not what happened to mine. Mine shifted fine and the TCC engaged ok.

The manual said that the TPS voltage should be between 0.2 and 0.74 volts at idle, although it also said that if it'* not in this range it should be replaced...it said nothing about adjusting it. I loosened the 2 screws and then started the engine and adjusted it (while idling) for about 0.47 volts at idle. It sure was difficult to reach the 2 screws! I was tempted to remove the whole throttle body again, but found that a long screwdriver worked. I should have measured the voltage before I started, but I forgot...oh, well, it seems to be working fine again...

No, it still has a rough idle, and the idle is still steady at around 750 RPMs.

The plugs and wires were replaced by a performance shop just after I bought the car (with 114,0000 miles), about 20,000 miles ago. Before they were replaced the engine stumbled whenever the boost was greater than 0 PSI, and since they replaced the plugs and wires it seemed to have a rough idle, but it'* hard to tell for sure because it ran so badly before that. The shop tech also said that maybe it needed a new coil pack and catalytic convertor, but then they said they were fine. I once measured the coil resistance, and all 3 coils had nearly identical resistances.

It gets between 18 and 21 miles per gallon with mostly moderate to heavy freeway traffic.

I only drove the car about 90 miles since removing and cleaning the throttle body last weekend, so I don't know if the fuel economy dropped, but it definitely didn't shift oddly during that time.

I'm amazed that the idle hasn't improved since cleaning the throttle body and IAC pintle...the throttle body was really dirty inside. One observation, though, is that on the '93 SSEi the throttle body was dirty but it looked mostly like carbon deposits. On the '92 SSE supercharged, it seemed to be mostly fuel deposits like you'd see in the throat of a carburetor. Does that mean anything?

I neglected to mention that the '92 was sold to me with a damaged corrugated metal outer sleeve on the EGR pipe under the EGR valve, and it leaks exhaust, but I've always thought that it carried exhaust back to the exhaust manifold rather than to the intake (the smooth inner tube carries the exhaust gas to the intake?), and the only negative effect of this leak seems to be an occasional EGR error for the largest of the 3 orifices. The dealer doesn't have this part in stock, but said they could special order it. The EGR code has only been set twice in the 2 1/2 years I've had this car. After the 1st time the error occurred, I removed the EGR valve and cleaned it. It wasn't very dirty, and the contacts measured almost identical to the one on my '93 SSEi. I bought a new EGR valve and installed it, but it didn't make a difference in the rough idle, so I put the old one back on.

The only other known problem is that supercharger nose leaks oil, but that'* another story...it'* an entirely rebuilt Magnuson unit that began leaking after less than 20,000 miles...

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!

That drawing of the belts looks accurate. The alternator is easy to remove, even on the supercharged model...but if you want to replace the water pump on a supercharged version, for example, you also have to remove the front engine mount (that'* documented in the shop manual ok) and the accessory bracket (and that'* not documented in the shop manuals I have). On the supercharged version it'* a rather large bracket, and in order to get it off you have to remove the power steering pump and then 2 hidden bolts in front of it, and drain the coolant and remove the 2 metal heater lines that go into the block, and there are a few other obvious bolts for the bracket removal also. The dealer said they charge 6 hours' labor to do the job - it took me 5 1/2 hours and it was my 1st time. At least I learned a few things in doing it myself.

I could go on and on...sorry if I've done too much of that already...

HEY, AFTER YOU RUN CAR THEN SHUT CAR OFF AND PULL VACUM LINE GOING TO FUEL PRESURE REGULATOR AND CHECK TO SEE IF THERE IS ANY GAS PRESENT!! IF SO REPLACE IT!!!

BAD EGR WILL MAKE CAR IDLE BAD ALSO!!!!

GOOD LUCK MAN