I've been having idle problems for a while now. Initially, it would only happen when the car was hot. When I would get off the gas, the revs would hang at about 1800 and stay there until I gave the throttle a blip, then it would settle down to normal. The problem kept getting worse (happening in more situations) and also the normal idle got faster (indicating 1000-1100). Eventually the engine light came on for an idle control error.
I took it to a shop and they told me the idle air control valve was bad. I replaced it, but it didn't fix the problem.
I took the throttle body off and after close examination, I believe I've found the problem. The throttle plate is worn a bit on the cable side, creating a flat spot at the 9 o'clock position. This is causing two problems: 1) The flat creates a gap where excess air can get past the plate causing the elevated normal idle and 2) the flat causes excessive drag between the throttle body bore and the plate which leads to it getting hung up in a very slightly open position.
After playing with it some, it looks like the wear was caused by the return spring biasing the plate to the cable side of the throttle body. The friction between the body and the plate caused the flat spot to develop.
Has anyone ever seen this before? I'm having a hard time coming up with something that would cause this to happen on my car and not all of them.
I'm not sure what to do to fix it. A new TB from Toyota is over $800. The plate cannot be bought alone. I could get a used TB and swap the plates, but there's no guarantee that the one I get won't have the same problem. Plus I tried to take my plate out but the screws must be permanently loctited 'cause they wouldn't budge. Some heat might solve that problem, though. I could also have a new plate fabricated, but that might be tough to get just right. Of course none of these solutions would prevent the problem from coming back. I've also tried attaching a tension spring to the cable pully that both gives it a little extra closing force and also pulls the plate back to center. So far that hasn't worked, though I'm still playing with it. Finally, theres the Blackwatch big bore TB for $500, but that's a lot of dough and I'd be worried that when I supercharge it would cause a reflash tune to not work out so great.