Hello all,

I have my blazer in the shop now as we speak with the mechanic running some diagnostics. I just did a full throttle body cleaning, along with cleaning the Mass air flow sensor. I also put in a new IAC and that is working correctly. I was told (by the mechanic) the TPS is working correctly as it is 0 when the car is in idle in park. My question is does the TPS HAVE to read 0 or can I adjust the base idle manually to bring my idle down a bit. It is running at about 898 RPM warm. It seems a bit higher than it should. It seems to kinda want to push through as I am coming to a stop. I feel like since the car is now getting a much better airflow (new air filter and clean intake components) the computer is at its threshold for adjustment of the IAC and so forth. So... is the TPS required to read 0. Thanks!

 

I high idle can be caused by sticking throttle linkage. A rivet missing from the throttle plate, or a vacuum leak. My truck idles around 650 rpm. My TPS reads zero at idle.

 

There are no vacuum leaks. No rivets missing and the throttle linkage isn't sticking nor is the throttle plate "stuck" open at all.

Mechanic said he can control the idle from 894 RPM to 1700 RPM only. He can't get it below 894 RPM though. Seems like it might be at a threshold for the computer?

 

The throttle stop screw is adjusted at the factory and should not be tampered with. There are no procedures for adjusting it in the GM "dealer issue" shop manual. Sounds like somebody "messed" with it On 1996 and newer, the IAC should be able to control idle speed from ~500 rpm to ~1200 rpm, (a difference of ~700 rpm). Yours is closer to 800 rpm which might not be a problem, other than the range is set too high. You'll need to make sure of a few things:
1) The seat in the throttle body must be clean.
2) The pintle valve on the IAC must clean.
3) The IAC must be good.
4) There are no vacuum leaks.
5) The throttle shaft is not bent or leaking vacuum at the shaft bushings.
6) The throttle linkage and cable are not holding the throttle open.

If those things are all good, the only way to get it back "in the ball park" is to command zero counts to the IAC using a scan tool, then adjust the stop screw to ~500 rpm. Zero counts will fully seat the pintle in the seat, disconnecting the IAC at idle, does not guarantee the pintle is fully seated.