Hi,
I have a 1968 fastback with a '93 5.0 engine in it. I have read through several "rough idle" posts on this forum and I'm not sure any of them have exactly my symptoms...so here goes...

The car starts with no problem. After a few minutes the engine will start rev'ing the gas. Not your typical rough idle (i.e. no violent shaking, coughing, etc.), it just revs the gas up and down mildly. It's like the computer is either searching for the right idle speed or the computer is having to rev the gas to keep the car running. When I drive the car it runs good. But, when I stop (like to make a turn, push in clutch and the RPMs drop rapidly down to idle) the car will sometimes stall on me in the middle of the road. Sometimes, however, the computer will catch it and start doing the rev'ing thing again. If the car does stall I can restart it with no problems and continue on.

Any ideas? Air flow sensor? Vaccuum leak? Bad EGR?

Thanks,
John

 

Even though the symptoms aren't exactly the same as others, I would still start with the simple fixes to see if that fixes the problem. Clean the IAC, clean the TB, check the TPS voltage, check for vacuum leaks for starters.

 

Follow Samseed101 recommendation, as long as the TPS is between .8vdc - 1.0vdc...it's OK + check the system for codes...KOEO & KOER. Code 29 and/or 67 (VSS and Neutral Safety Switch/Clutch Pedal switch)....affect the idle strategy "selection" by the ECM and will cause the problems you're having.

 

My guess would be a ground on the computer, not hooked up. I had one do the samething.