My brother has a 94 Z28 with some idle problems, I got him to send me a datalog of his engine and his IAC numbers all over the place. They start at 156 and then are from 73 to 100+. Is this normal?

 

I think around 32.

 

When engine is at operating temperature it should read between 20-40

 

If the car has heads/cam or some power adder then the IAC counts could go that high.

 

It has a cam, CC304 if I recall, but stock heads

 

He has a vacuum leak

 

Why would a vacuum leak cause the IAC to open up, and provide even more air?

 

Yes it's a CC304 cam, with stock heads. If anyone wants to see the log file, here it is.

 

Anyone else? Also, the problem is only in gear, not neutral or park.

Other problems:
Bad gas milage
Sometimes a light throttle stuble only in 4th gear around 45-50mph.
Occasional backfiring at higher RPMs, espically when cold.

The plugs and wires are pretty new, and O2 sensors were just put in.

 

We all got to take our lumps especially when we have a brain fart. He said higher but I saw lower.

What you could do is remove the IAC and see if it is actually moving when commanded by the PCM. I use a pencil with one of those push on replacement erasers trimmed to fit in the IAC pintle hole. If the PCM is responding to differing demands to change the idle, it will move the IAC pintle in response to either slightly restricting or unrestricting the IAC passage with the pencil eraser. This will allow you test the entire IAC system.