IAC, TPS, idle shenanigans

[ACLR8R]

OK after headgasket replacement the car has idled rough, and sometimes not at all. The IAC is really high reading in the 90-150 range, the TPS wanders around (.36, .44, .38, .42. etc) with just the key on, when I unplug the IAC this stops and it is steady at .38. I tried to get the IAC down but I now have the idle screw all the way out (not touching the linkage) and the car is idleing around 800 and still fairly rough IAC still low to mid 100's. Should I replace the IAC? Something else?

I have tried a new TPS and it did nothing.

Thanks

 

[87NAT]

The adjustment screw for the butterfly should be sticking out with only 1 1/2 threads showing (pointing to radiator). This is your "ballpark" setting to fire the car up. When adjusting the IAC make sure engine is at operating temps and let the car idle for 2 minutes after each adjustment. The ECM will "hunt" for the right idle and settle in. After 2 minutes shut off the car and restart. Make another adjustment if necessary. Remember to set the TPS with each TB screw adjustment. It just takes a little time to get both where you want them. Remember you cant set one without affecting the other.


IAC idle values 10-30
TPS .42-.45

 

[Just a Six??]

I went thru this myself & still am to a degree. Works fine when driving but after idling too long it shoots to 150. I have a few threads about it on the other board. I learned from John Spina (Caspers) that the ECM has a separate driver for the IAC which can burn out with a major short, or bad grounds, power surge etc. There is also another thread about it going on now. I had a lot of good responses for testing etc. Go there & do a search.
Hope this helps!

 

[TurboBuRick]

Bad sensor grounds? On the back of the passenger side head are a bunch of grounds. Make sure they are clean and tight.

My $.02

 

[ACLR8R]

Bad sensor grounds? On the back of the passenger side head are a bunch of grounds. Make sure they are clean and tight.

My $.02

Thanks, thats the first place I went. They are fine.

 

[GNRick]

It would help if you drive the car for 10 minutes then come back home and check the iac.

 

[83ttypecooled]

Hi,
So your IAC seems uncontrollable, always inputting more than needed, correct? Idle is rough, and TPS is fairly regular,within 0.05 v or so? Stop sweating the little stuff, keeping in mind that you just replaced head gaskets.I would switch gears, and start looking for vacuum leaks.The valley gasket could be leaking under the intake.Pull the pcv and hold your finger on the hole. Can you feel vacuum? Your motor is a likely candidate for this possibility. Good luck!