idle problem

[gc96z28]

off of a recent header install, when the car is in gear and at a stop, the idle jumps between 500-700 rpms. I had my computer tuned by pcmforless and it didn't fix the problem. Could it be the existing 02 sensors or spark plug wires?

What could it be.? Whatever it is it is throwing the SES light.

[Jeff_in_Atl]

I don't know if this could be similar but I converted my 85 Mustang GT to the Holley projection fuel injection. I put the O2 sensors way down underneath the car. . The cars idle would very about 200 rpms in about 2 second intervals. I called Holley and they said I had the O2 sensors too far away from the engine which caused a delay in the O2 readings verses the actual combustion.

I just was wondering if your O2s got moved down the exhaust and could be doing the same thing.

[Injuneer]

If the SES light corresponds with the problem, why not have it scanned? That might just point you in the correct direction. Some auto parts stores will scan your OBD-II 1996 for free. An OBD-II code reader can be purchased from Harbor Freight for $40.

Have you ever cleaned the throttle body, including the IAC motor and the idle air passages? That's just a wild guess..... a scan would eliminate the need to guess.