TPS, IAC, or Something Else?

new 09/28/2004

I have an issue with stalling and unsteady/surging idle while in gear. The symptoms don't fit exactly fit the stuff I'm reading on the website for IAC or TPS problems.

I've pulled the CAI and reinstalled the Porterized setup to rule out MAF reading problems (I had been informed that the MAF will freak out if it is too close to the TB.) At any rate, that did nothing to help. The car accelerates and cruises perfectly. The idle is perfectly normal when in P or N. However, when coming to a stop, the car will occasionally stall, and when in D, the engine speed will bounce up and down from 500-1000, sometimes cycling once per second, sometimes slower. Sometimes the car behaves fine.

I have pulled, cleaned, insulated (w/ dielectric grease) and reinstalled the MAF, TPS, IAT, and IAC connections to no avail. The stuff I'm reading on the website about the IAC and TPS seems to be related, but not exactly what I'm getting. Also, the car doesn't idle any differently with the TPS plug pulled. I thought it was supposed to stall when you pull the TPS plug (?) The idle drops down to a steady 500 or so when I pull the IAC plug. I have already thoroughly cleaned the IAC valve, so the next step would be replacing it, but it's too expensive for me just to assume that the IAC is the problem.

Dan Carman
'97 PG

Don't use too much dielectric grease.

Paul Nimz

Well, I checked out the IAC again. It was pretty clean, but I used up 3/4 of a can of carb cleaner cleaning it up again, and now the thing is SPOTLESS inside. I don't see how it could be failing, but the wavering idle and stalling problem is still there. It seems to only do it when the engine is warmed up and I get a few blocks from home, and only when in drive. I'm going to start checking coils, but time is of the essence right now. If anyone can help me out by finding me a loaner TPS and/or IAC so I can diagnose the problem, I'd be grateful.

Thanks,
Dan

Just managed to find the time to check the front coils (the back ones are fairly new @~10K miles, so I doubt they are a problem) and they all look perfect and pass the "shake test". Someone "borrowed" (OK, stole) my nice multi-meter, so I'll have to wait until I find the $$$ for a new one to give the coils a more thorough test.

The idle is smooth... It just has a tendency to start loping up and down once in a while. When the coil in the back row shit the bed, I could feel the misfire from time to time. So it's either not a coil failure, or the coil failure just hasn't gotten bad enough to be noticed all the time, or it's a different type of coil failure altogether. It hasn't done anything erratic in the past 8 miles, but today at lunch it crapped out twice at stop signs, even though the idle seemed to be behaving pretty normally. The wiring harness to the front coils seems to be OK--no signs of melting or other damage.

Dan

We evidently still don't have a happy ending for Dan's and frankly my idle problems. I must admit though, mine has settled down and is now nowhere near as drastic as Dans. The hunt will continue.

U.L.

10/04/2004

Well, I cleared the KAM by pulling the EEC fuse on Thursday (thanks to Larry reminding me.) I haven't had any problems since! This is a bit confusing, because I'm positive I pulled the fuse after replacing the TPS, and I'm pretty sure I did it again after replacing the IAC. But in retrospect, the IAC was a rush job and maybe I left out that critical step. Since the car was still acting goofy at that time, I just assumed that the IAC hadn't been the problem, but maybe the PCM was just ignoring the IAC w/o tripping the CEL. Looks like clearing the KAM set things back to default and the PCM is now treating the IAC as a trusted part of the engine control system.

I guess I'll just hold onto the new CKPS for a rainy day.

Thanks to all who contributed! I know many of these suggestions were already on the site, but with my symptoms being just *a bit different*, it was great to have the support and suggestions of the group.

Dan Carman
'97 PG no longer embarrassing me at stoplights.

Well finally a happy ending for Dan. !! Glad I could help sir.

U.L.

Contact Information