I have a 1988 formula 350, and i seem to have a problem where at times the car will run unbelievably great, others it will not run at all or barely idle. The other day i replaced the IAC, which didnt help at all. Then i read that a rough idle, and stalling may be caused by some timing error in an electronic part. So i dissconected the EST and it started right up and idled smooth for 5-10 seconds and went to a rough idle. So i ran it 3 times without the EST bypass plug connected, then i reconnected it and it still starts right up and idles smooth for 5-10 seconds. This comes of as really odd to me, it wouldnt run at all or barely idle before, now i have a consistant start and idle. This leads me to believe either i have a malfunction in the perhaps ICM,EST, or ESC. Or that i have a wiring problem, possibly blown fuseable link, any thoughts on what may do this would be of much help. Some days it will run like a dream others it will not run for my life.

thanks

 

does the RPM bounce around at all? If not it might have something to do with the timing and i'd check into that.

 

yes timing bounces sporaticly, and its not the fuel pressure, or spark, they are both consistant and steady, i nearly eleminated it by dicconecting a wire (supposedly EST bypass) a yellow and black one near the brake booster next to the block of the engine. After that it ran good for about 5-10 seconds everytime consistantly. Im confuesed about what to assume on that one though.

 

If you think it's a wiring problem look into the engine heat sensor. I don't know where they are on the 3rd gens but on my LT1 it's on the water pump, i'd assume it's in the same spot. It might be something with the wiring on that, cause if the cars computer thinks it's at a different temp then what it's really at, it could screw up air to fuel ratios and make it run bad at times. I'd start checking all wiring and/or sensors and see if the connections are corroded or anything.