iac, what does it affect?

454ss · April 21, 2004

what all does the iac affect? what does it cause the engine to do when it goes bad? i have a 1997 gmc k3500 with a 454 that has a very inconsistant idle when it is first started, it will rev up high then down almost to the point of stalling. it does this for 5 minutes or so then smooths out. could the iac be the cause? the egr valve has been replaced. thanks for any ideas.

Frank S · April 21, 2004

It can throw your mixture way off causing bad idle such as too high or too low,things like that.

If it's running up and down and you think it's a sensor make sure that you also check the throttle positioning sensor.My ZR2 was acting exactly how you describe and that turned out to be the problem.

454ss · April 22, 2004

i replaced the tps last night, no change, when i started the truck this morning it acted the same way.

Frank S · April 22, 2004

Well realistically,either one of them should be throwing a code through your OBDII if one is malfunctioning.If the SES light isn't on then most likely no code is being sent unless the light isn't working for some reason.

I did know a guy who also had an eratic idle on a 454 powered Suburban and it turned out to be a faulty throttle body gasket.It was a late 80's/early 90's so it may not be the same problem you're going through but I'm just offering suggestions.

Butch 02 Denali · April 22, 2004

I have a 1990 454, and the TB gaskets are a common problem. I know when I need to replace it when the idle goes crazy when cold! I'm not sure if the 95 has the same TB set-up, but it does sound like a vacuum leak that seals itself when it warms up.

Butch 02 Sierra Denali