Backfiring Vortec 4.3

[Jobey]

I put it on the scanner again and it said iac (idle air control) not responding. So I put in anew iac valve and then the idle goes straight up to 3 grand. Took that one out cause I thought I got a bad one and the second one did the same thing. I’m thinking that it’s whatever controls the iac ( maybe computer?). It doesn’t make sense that the intake gasket would be bad cause it was running perfect when I shut it off at night then morning it started doing what it’s doing now. When I took out the old iac the nub coming out of it was fully retracted in and the new ones are all the way out and they didn’t move after I put them in.

 

[Schurkey]

Use bi-directional control on the scan tool to adjust the idle speed.

If it won't adjust...the computer, the wire harness, or the IAC is faulty. Perhaps a combination. Less likely to be an IAC since you've tried three of 'em--original plus two replacements.