I have a 1990 L98. I have driven it twice lately and both times I have been left stranded. The problem is while driving, when I push the clutch in to stop or just coast, the RPMs fluctuate between 500 and 900. Sometimes it steadies itself out at 750 other times it stalls. It seems this really drains the battery too as I had to be jump started or push started most of the time.

I had the alternator tested and it came back ok. I had the battery checked and it was ok. I had the store put a full charge on the battery. I went home, installed the battery, started the vehicle. The volts from the alternator were 14-15, the battery was about the same. After the car warmed up, the same thing happened. I revved the engine and it fluctuated between 500 - 900 and would die.

Does anyone have any ideas of what to check next? I don't have any codes. The engine was rebuilt in 2007 and a bunch of electrical problems were fixed recently. When the engine is cold it seems to idle around 750 rpm, after it warms up it wants to idle around 650-700 and it feels like there is a miss as I can feel a slight engine vibration.

 

How old are the spark plug wires? If it is missing, it could be a plug not firing and causing rough idle.

 

Do a tune up.......... Wires, plugs, cap, rotor and fuel filter.......... While your at it get a modual.......... Take it from there........ If its its anything beyond that good luck..............