So I bought a 91 4 door the other day and it is having some strange idle problems. It idles fine some times, but other times it gets a fluctuating idle. The idle spikes at around 2400 rpms and drops down to 500 and while its doing this the check engine light goes on and off.

Its really annoying as this causes the car to die randomly while at stop lights.
The motor is the original D15B


I was thinking its probably something IACV related but if anyone else has experienced a similar problem, please let me know how to correct it.

 

you would be right....its either your IACV of TPS

 

Check all ur vacuum hoses first to make sure there's no leaks and also make sure ur coolant system doesn't have any air in it, that will give u a jumpy idle also.

 

Well, I just now got around to messing with it. Today the CEL is staying on, before it only came on while the car was idling weird. Today's idle is at 1900 rpms and won't go any lower. Oh and it won't rev past 3200 rpms. It sounds like its hitting fuel cut off.

Any ideas?