I have a 91, stock L98 and I was driving in a traffic jam and the idle started to slow down and was a little rough. The next morning it felt like 2 cylinders were missing. After it warmed up it was idling rough and still felt like 1 cyl was missing. I replaced the plugs, rotor, cap and swapped out the coil and ignition module with my son's 88 L98. The wires are 1 year old and the ohm readings were good. The magentic pick-up is only 1 yr old. I put an old plug and ground on each wire and all cyls were firing. The fuel injectors are 1 yr old and I tested them hot and cold at 16 to 16.5 ohms. The fuel pressure is 38 PSI and hold pressure forever when the engine stops.

How can I tell if the injectors are pulsing? I put my finger on the side of each injector and I think I can feel the vibration but I would like to test them more accurately. Just about every sensor on the engine was changed last year. The car had been running great until the traffic jam. I have a 160 degree thermostat and the engine didn't even get hot. Just warmer than normal. We did have a cold rainy night after the traffic jam. Could moisture cause a permanent problem? I thought it would dry out after a while if it was a moistrue problem.

Anyone have any suggestions?

Thanks, Mickey

 

Fuel pressure sounds low to me. Isn't it supposed to be over 40?
How about the fuel filter, has it been changed lately?
Water in the gas?

 

It sound like a vacum leak to me. You didn't mention if the check engine light was on or not.

 

I assume you tested fuel pressure with the vac line connected, hence the low reading. With vac disconnected & plugged it should read 44psi.

When I get a miss I first clip a timing light onto each wire in succession to locate an ignition problem.

 

I do not have any codes and the fuel filter was changed about 2,000 miles ago. The fuel pressure was checked with the vacuum line connected. The idle is loping and the exhaust doesn't sound like a miss. I have tried to locate one cyl with a miss but pulling a plug wire on any cyl doesn't seem to make a difference.

Thanks, Mickey

 

Not that this is your problem but it was mine. I have a set of Bosch wires on and the exhaust manifold melts the rubber plug caps then it starts arching to the manifold. Check it out in the dark. Real dark. Check and see if sparks are flying.

 

The engine temp sensor is 1 yr old. Could it go bad and cause this problem? How can I check the injector pulse? The TPS checks good and the idle air valve is 1 yr old and the idle rpms are OK.

Thanks, Mickey

 

im having the same exact problem. i replaced my plugs wires, cap and rotor a few months ago. the miss or what ever it is seemed to get better. then this week i was getting on it hard and the miss came right back. ive checked in the dark to see if the wires were grounding out. i didnt see anything. if you figure it out let me know. or if i get the problem fixed ill do the same.

Paul

 

Done everything, my still idles like crap. Just turn up the radio. It takes my mind off of it.