: High idle after TB cleaning - 96 Eldorado (solved)

01-22-14, 03:07 PM
just to throw this out there:

cleaned the throttlebody and iac yesterday, didn't take out the tb for that, only unscrewed the maf (cleaned it as well) and the iac and cleaned it as good as possible with a rag and carb cleaner. so, after putting everything back together she started to idle at like 1200 rpm and showed pc0507 (idle too high), together with a "service idle control" message. before the cleaning everything was working fine, so i figured it must have something to do with what i took off. so i played around a bit with the iac valve, pulling, pushing, turning and so on. checked for something that might block the throttle, like a piece of rag or carbon residue left over. found nothing like that. took her for a spin, thinking some adjustments might be necessary and over time driving around idle may get normal. well, didn't happen and i called it a day.

today i took everything apart again and inspected again and looked around here to see if i can find something out. not really... so i figured that the iac actually is working, since i can feel the movement and it most likely closes completely, that not being enough to restrict air flow. or a vacuum leak... so i went on and sprayed (starter spray) around, no obvious leaks.

then i thought maybe the throttle stop screw (red circle in the pic, 15tx) has been fooled around with sometime and probably the clean tb lets more air go through than usual and that's causing the high idle. and sure enough, after like 2 turns out and making sure that the throttle still is stopped by the screw, rather than the tb itself the idle went down to what it's supposed to be and the iac is regulating now.

i'm just writing this up for somebody that has excluded everything else on their search for high idle after tb cleaning and can't be sure that this little screw hasn't been fooled around with. generally it has to be left alone the way it left the factory, but if some shade tree mechanic at an earlier point thought it's the idle set screw, then you might as well have to look into that, if everything else is working ok (no vacuum leaks, tps ok, iac ok, etc.)


01-22-14, 04:56 PM
Nice writeup. I'll move this to Cadillac Tech Tips for everyone to use. Thanks.

01-22-14, 08:38 PM
Well I'll be dipped. Never would have thought about that. Nice catch.

01-23-14, 11:00 AM
thanks guys. i was surprised how much of a difference in airflow this tiny throttle movement can make...