So I recently picked up a 97 z28. Mods are a hotcam kit, longtubes, cai, etc. Typical Bolt on car. I've had a issue while driving over 40ish mph where the car surges while coasting and idles low at stops (500 rpm or so). I've tried to read iac counts but I can't see it using torque pro for whatever reason. I've checked for vacuum leaks with a smoke machine but found nothing. My guess is in the tune (which I have no idea who's tune it is, previous owner couldn't remember) or it's a egr issue. The egr is still there however the metal tube going from the intake to the manifolds is unhooked and plugged. Any ideas? Tps voltage is in spec and I have reset the iac numerous times with no effect.

 

Manual or auto trans? Programmed idle speed is often different based on trans type. But then we don’t know what the tuner set the idle at. Additionally, EGR system doesn’t operate at idle.

If EGR pipe from #8 primary to right rear corner of intake manifold is correctly blocked off, no way EGR system itself can cause these problems. If it isn't done right and there's a vacuum leak, possibly could contribute to the problem. Normally, the pipe is deleted and a blocking plate is placed over the opening in the manifold. Is the EGR valve still there, or has that been deleted, and a blocking plate placed over the opening in the manifold?

Is there a code for the deactivated EGR system? If not, the code was probably “programmed out” by the tuner. And he should have cleaned things up in the tune so that the timing, etc. would be correct without the changes that the PCM makes when EGR is activated.

EGR is typically used when “cruising” at moderate speeds, below 3,600 RPM.

Is the EVAP purge system still operational? That can cause vacuum leaks when it operates.

 

Sorry I forgot to say it is a auto. Egr valve is still there, but no codes. I never considered the evap system. I have noticed what seems like a abnormal amount of pressure release when the gas cap is removed.