IAC problem 1986 GM 5.0?

[Bud]

Hi folks
I have a 1986 GM. When you first start it it idles down ok till it warms up then the idle increases. No tac but it seems to increase several hundred rmps more when warmed up.
Does this sound like the IAC valve or something else. I pull the plug on the IAC after engine is warm and it dies. Mech checked for vacume leaks and says there are none. He said the butterfly was the prob but I don't think so.
Help I'm afraid this will hurt the transo!
Bud

[murphmobile2]

Have you tried re-setting your idle? Definitely can't hurt any.

[Bud]

Have you tried re-setting your idle? Definitely can't hurt any.

If you mean the idle adj screw it doesn't respond when I turn it out to slow it down

[Bud]

Maybe I should rephrase my question to: What would make my car (86 GM 5.0) idle fast after it warms up. Does fine till then. Idle screw has no effect after warm up.
Thanks
Bud

[kodiak]

are you turning the idle screw or the fast idle screw for when it's warming up?

Sent from my '85 Lincolin Town Car

[Bud]

Kodiak Im not sure. The one I turn is below the throttle body pushing against a little odd shaped plate. Seems to be on the same shaft as the butterfly

[porschpow]

Didn't know there were two screws. I thought there was just the one under the Throttle body by the accel cable

[Bud]

porschpow that's the only one I saw also-but I'm only a shadetree mechanic

[sly]

there's only one idle screw on an EFI and it is not an idle set screw, it's the throttle valve stop screw. It does not adjust the idle. The IAC controls the idle. If you have adjusted that screw, you've messed it up. There is a procedure to reset that to the proper setting, but it's involved. I'll see if I can find the post that has the page about it.

[miamibob]

Wouldn't be messing with the idle screw unless I REALLY had to (with a DAMN GOOD REASON)!

[Bud]

there's only one idle screw on an EFI and it is not an idle set screw, it's the throttle valve stop screw. It does not adjust the idle. The IAC controls the idle. If you have adjusted that screw, you've messed it up. There is a procedure to reset that to the proper setting, but it's involved. I'll see if I can find the post that has the page about it.

Sly I have messed it up then-I have also screwed around with the throttle position sensor so any tips about that would be appreciated.
BTW what controls the IAC valve? It reacts when you unplug it so I don't know if its bad. Also I took it off and cleaned it out but it made no difference-it wasn't gummed up anyway.
Thanks
Bud

[85crownHPP]

Could be a bad air charge temp sensor, they are cheap and pretty easy to get to. Its in the driver side lower intake, near the fuel rail under the TB.

[sly]

the ECM controls the IAC. I'll try to remember to get that diagram that shows how to set the idle posted. It's a bit of an involved procedure.

[Bud]

Could be a bad air charge temp sensor, they are cheap and pretty easy to get to. Its in the driver side lower intake, near the fuel rail under the TB.

sly


the ECM controls the IAC. I'll try to remember to get that diagram that shows how to set the idle posted. It's a bit of an involved procedure.
Thanks for this and all other responses-I was seriously wondering what controlled the IAC. Hope I don't have to replace that!!

[85crownHPP]

You can try giving the IAC a few smacks with something solid when its acting up. If that repeatedly clears it up, pretty safe to condemn it.