From what I have researched on here, it is a problem with one of the following:
-IAC valve
-TPS
-intake gaskets
-O2
-PCM tune
Anyone else have something to add?
GEN II:
Reviving an old post to add some positive results. I checked all of the above and yes, the performance PCM tune was the beginning of the problems. I went into the tune settings and there wasn't anything there that I could see causing a problem. I replaced my IAC valve, cleaned my TPS, check the intake and vacuum lines with starting fluid and replaced O2 sensors. I also have done over 1 1/2 years of trial and error testing to try to determine the cause of my fast idle being erratic until I get down to below 10 mph and then it settles in at around 600 rpm. The fast idle when I pushed in the clutch was swinging between 1,000 and 2,000 rpm. This happened in ALL conditions - open loop, closed loop, with and without AC, with and without brake being applied. I tried every variable I could think of to try to narrow down the cause. This has been going on for over 18 months, guys! If I took the car back to stock tune, it stopped, but I didn't want to give up the HP that I picked up with my tune.
SUCCESS! I was checking the oil last night and I remembered having read something about the left (driver's side) throttle body should open 'slightly' before the right throttle body. I hadn't touched the little set screw for the throttle bodies since they seemed to be in perfect sync.
I SHOULD have touched the throttle bodies!! I loosened up the set screw to allow the left to start to move just a hair before the right. Wiggling the shaft that controls that gave back a very slight 'slop' between stop and start when I was done.
RESULTS: I drove the car for 60-70 miles today, both highway and city, hot and cold, with and without air. Every time I pushed in the clutch at speed, the tach held at 2,000 rpm (no stuttering) for the first 30 miles. After that, the learning mode of the PCM took over and dropped that high idle down to 1,500. It stays there until below about 10 mph and then it drops to a steady 600 rpm. I think this was the problem all along .... and such a simple fix. I can't believe that the shop that did the tune didn't check that when I complained for 6 months about the problem that their tune had caused.
I hope someone else can gain from my 18 months of hating to pull to a stop next to another car ... it sounded like I was revving my engine as I slowed down. I'll let everyone know if it changes, but I think I'm good on this issue.
