I have a 91 Z-28 w/ 5.7 TPI (35K miles) that just started running rough at idle and also the engine surges about 100 RPM. Lastly, it will sometimes hesitate a little bit on acceleration but this is only momentary.

The surging seems to be worse in neutral or park, but the rough running seems to be worse in gear if just idling the car or if stopped with foot on the brake.

As best I can tell, it seems to run OK on the highway.

The SES light comes on for the key-on bulb test, but is off during driving and no codes are set.

Any help would be appreciated.

 

First off - have you changed anything or done anything to the car recently?

If it's been a while since a tuneup, that might be in order now.

If neither of the above....

Number one item to check is a vacuum leak. Look for a loose or cracked vacuum line.

I had my car down almost a week for a similar symptom. Ran fine to work, would hardly idle and ran like a dog when I drove it home. In my case the IAC froze up. The ECM was still showing that it was moving, but all it was really reporting was what it told the IAC to do. No check engine light, but replacing the IAC put it back where it was.

Good Luck!