2004 Ecotec Cavalier M/T with GMPP S/C, 2.9" pulley (from 3.3" standard), 42lb injectors. Otherwise completely stock.
The car ran fine, but very rich (13 MPG highway), up until I recalibrated it (thanks for the file Brett!). I finally got around to installing a wideband O2 sensor on Saturday so I could tune the car for the smaller pulley and larger injectors. I had already got the PCM calibration done by GM, so I had to install a salvaged PCM.
The salvaged PCM is from a 2004 Sunfire A/T. I told the guy at the yard I needed one from an M/T, but apparently he ignored that. So I tried the tune anyway, and as I expected it worked. I zeroed all the A/T tables and turned off the A/T codes. Idling in the bay it was great, better throttle response, didn't bog down before it revved like it did before the tune. Driving out of the shop, it idled at about 2k RPM until I came to a complete stop at which time the idle dropped smoothly down to where I set it at 1,000 RPM. I shut the engine off and restarted it, drove around the parking lot, and it dropped down to 1k RPM as soon as I pressed the clutch.
I went to the auto parts store to find a glass fuse for my power inverter, which I then found was junk... new right out of the box. On the way there, it would idle around 1,750 RPM with the clutch depressed above 30 or so MPH, and would slowly drop down to 1,000 RPM when I stopped. No slow decay as I slowed down, just 1,750 --> stop --> drop to 1,000. Leaving, I turned on the A/C for the drive home, and the RPM shot up to 3,500 with the clutch in. I turned it on and off a few times and the RPM was only high when the A/C was on. I turned the engine off and restarted it a few times, it did nothing for the high idle with the A/C on, but it started idling at about 2k RPM without the A/C on again. Later that night before I went for a drive, I lowered the idle VE thinking maybe the PCM thought there was more air than there was, adding more fuel, and then for some reason stepping up the IAC to get it close to 14.7:1. I thought that helped, but I then found that whenever I write a calibration it fixes it for a mile or so, then starts doing it again. After about 15 miles it gets better. As soon as I turn the key off and restart, it goes right back to the high idle. Doesn't matter if it's off for 10 seconds or overnight.
Has anyone seen this happen before?
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'04 Cavalier
2.2 Ecotec Supercharged w/ 2.9" pulley
Charge air cooler
Poly bushings - lower control arm and engine/trans
Have you tried disconnecting your battery for 30mins? I know it's an odd solution, but I know that has helped quite a few people with some strange idle issues.
Check your HPT Scanner and see what the throttle is reading when your car is idling like that. If it's reading something more than 0, check out the throttle cable, your throttle pedal, the throttle bracket on the tb, and lastly take off your intake and have a look at the throttlebody itself and see if anything is up. If the sensor is spiking, its likely TPS related though I cannot see that causing the problems you're currently having. Lastly, what does your vacuum reading at idle look like. Sorry if I missed anything in your post that stated any of this already.
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