idle low...but runs like a champ...

[chevyndn]

well i have a question about the idle in my 1992 k1500 blazer. it has a 5.7 in it and it idle about 200 rpm when in gear after its warmed up, but if i put it in park or "n" it idles back up to 600-800 rpms. it dont bother me since it dont hesitae when i hit the gas. i was just wanting to know if anyone else has this problem.

[ChevyTech]

Sounds like it could be a bad IAC

IAC (Idle Air Control)

The IAC (and computer) control the idle speed.
The IAC (and computer) is what gives the engine a “fast idle” speed when started cold.
The IAC also supplies more air to compensate for the extra load when the A/C is on. If you have A/C and turn it on while listening carefully you should be able to here the IAC controlling the idle as the A/C clutch engages and disengages.

IAC passages can get plugged up with carbon or muck. The IAC units get erratic as they get old and stick. Use care when cleaning the IAC. The IAC should not be cleaned with carburetor cleaner or other harsh chemicals. If the chemicals get down inside the IAC, it will damage it.

To clean the IAC, you should remove it, and use a wet rag to wipe the tip of the plunger, while holding it with the plunger pointing DOWN. Be careful, the IAC will break easily. It is aluminum. Clean the passages in the TBI unit while you have the IAC removed.

The IAC gasket should be installed dry.

Don't use a big wrench to tighten it. Just a little more then hand tight is enough.

I do not suggest unscrewing the pintle (plunger). If you don’t get in back in far enough, the IAC can get damaged if the “pintle” (plunger) bottoms out in the TBI, when you screw the IAC back in.

When the engine is started, does the engine have a fast idle that slows down as it runs? The IAC (idle air control) is what gives the fast idle speed when started cold.

[chevyndn]

I have already check the iac, I forgot to mention that.
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