I had a GIAC chip installed, and went over to the BFI stage 2. Once running, the car ran fantastic for about 4 days. I was really pleased that the rev-hang issues (revs hanging up between shifts) were gone (when I let off the throttle, the revs dropped quickly back to about 1050rpm idle). Then a problem developed suddenly where the rev-hang returned and when coming back to idle, the engine will float between 1500-2000rpm for a few seconds before returning to idle. The rev-hang is much more noticeable now than when the GIAC was installed. When cruising around 1500rpm, I can feel the motor trying to pull gently towards 2000rpm. Intake system is clean and no check engine light. When I put the GIAC chip back in, it seems to run just like it used to (same amount of rev-hang, returns to idle quickly). Re-install the BFI chip, and the problem is back, even after clearing the ECU via VAGCOM (just to clear whatever learning sequence it does). Thus far BFI doesn't have an explanation. There aren't any vacuum leaks. I took the cover off the idle control motor, cleaned it with contact cleaner, and nothing appeared visually broken in there but it's obviously not serviceable. The only thing I can think of is the throttle body needs to be replaced, but I don't understand why the problem doesn't show itself with the GIAC chip installed. I can only surmise that the BFI chip is actuating the idle control motor in a different manner and the original idle control stepper motor can't keep up?
I posted videos to exemplify the problem.
What the hell is going on? I'm super frustrated because the car ran the best it ever had for about 4 days.. and now it's all gone to **** again grr.