I am having a head scratcher. 92 z28 has sparatic problem where at a stop light and sometimes driving, the rpm will swing up and down and sometimes idle up to 1600 rpm at stop light. I have replaced the distributor, checked the ground wires on back of motor and by battery and repaired one bad ground wire. There are no codes in the computer. O2 sensor has been replaced, air idle motor removed and checked, ok and working. Knock sensor scanned fine on operations, checked all over for vacuum leaks and none found (used up 2 cans of carb cleaner looking)...... Unhooked and plugged brake booster line and no difference apparent so rehooked. Carries 38 lbs of fuel pressure. Map sensor appears to be fine and operating. Hard to inspect egr valve but car is not smoking or burning unusual amounts of fuel. Plugged reman ECU in and no change. Installed new fuel filter. Not sure what else to check. Car may run fine for awhile and then, seems to be at stop light more than anything, engine will surge to about 1600 rpm, and then maybe fall on it's face. Sometimes it will stumble when driving and then clear up and run ok for awhile. I am out of ideas but would appreciate only knowledgable replies please. Once again, vehicle scans with no codes to be found.......Thanks for your thoughts, Scott......PS.....not the car in the pics....

 

have you checked tps voltage? mine had this prob ,readjusted tps it stopped,later jimmy