help I tried everything! High idle
95 Talon Tsi
Everything runs fine, strong boost, smooth idle on cold start... except sometimes an anomoly occurs, which I think i've narrowed down to happening only when I've driven it 10 miles or so, turn the car off, then start it again. The idle rises when i start the engine to 1100 rpm, then it'll climb to 1500 ish, then it will rev itself between 1200 and 1500 up and down, up and down, up and down. Sometimes it will just idle at 2800 to 3000rpm. When I start the car cold, the idle is nice and crisp staying at around 750 -800. I can drive it for almost an hour straight with no problems. Cannon ball runs down the highway, stop at an off ramp and it sticks at 750 like that's it's job. But i turn the car off to go into the store, and when i turn it on again, the idle starts doing it's thing again. At least it's not doing the annoying up down thing first thing each morning.
Checked all the vaccume lines, as much as i can see, and everything looks like it's in shape. Took it to advance auto for the free code scan service. Scanner said P0505 Idle Control System Malfunction. They kept saying they think it's the TPS I thought no kidding! Opened the haynes manual, it says the code P0505 means IAC Valve System Fault. So i went to the junkyard and snagged a new-to-me IAC Valve. I swapped it in and turned on the car. It started and immediately idled a little low and a little bumpy like it was choking for air. Then I thought to unhook the battery terminals for 15 min to reset the computer and let it calibrate itself. Hooked them back up and started the engine again. Up down, up down choke choke, .... at this point i thought WTF!? Then i tried to listen for the IAC Valve motor make sound like the manual says while an assistant turns the ignition on and off without starting the engine. Each time i heard it make more and more movement. Finally after enough on and offs it sounded like it had worked it's kinks out. Started the engine and it worked like a charm. Mabee it calibrated itself? Dunno but I thought it was fixed. Went to the store, came back to the car and turned it on..... high idle thing again. Very frustrated at this point. TPS? IAC still bad? PCM?