Hey guys.. I've been slowly getting my 92 NA FC back to driving condition after it sat around for more than 2 years. I drained the gas tank, and refilled with fresh gas. New plugs, coolant, etc.. just basic stuff. The car is a pain in the *** to get started.. one or two cranks are more than enough to flood it.. which I don't mind too much at the moment, but....

The problem I'm having is that after the engine warms up after about 15-20 minutes, the idle jumps around from 100rpm near stall to just over 1000rpms. Before it is fully warmed up, it goes through normal warm up RPMs.

If the mileage on the odometer is correct, it has just over 80k miles, and the engine was rebuilt some 20k mile ago according to the previous owner, or as far as I can remember from what he said 2+ years ago.

Any ideas? Search did not come up with any low idle bouncing.

-Bart

Edit: Forgot to mention.. When the engine is still warming up, I can give the car throttle and it sounds smooth. Once it warms up, theres a mild low rpm hesitation.

 

Sounds to me like the water thermo pellet isn't functioning properly. A simple fix/check is to set the tps to spec, get a multimeter or a test lamp.

 

water thermo pellet? whats a pellet?

 

Bump! Somebody has to know whats up..

-Bart

 

Cars not throwing any codes. Bump!

-Bart

 

I'm not sure the thermo pellet is your issue here; seems like your car is warming up normally.

Bouncing idle is usually caused by a vacuum leak. There are several ways to hunt leaks, one of the easier ways is to get an old stethoscope, lop the end off so you just have hose and listen to various vac system joints while the car is running and listen for hissing. If you don't have a stethoscope (who really does anyways?) just use a length of rubber tubing, sticking one end in your ear.

Out of whack TPS could also be a problem. do a search on how to set it. been covered many times before.

 

*******The problem I'm having is that after the engine warms up after about 15-20 minutes, the idle jumps around from 100rpm near stall to just over 1000rpms. Before it is fully warmed up, it goes through normal warm up RPMs.**********

What seems to be happensing, after the engine gets hot, and the idle is going waaaay down to 100rpm and then going back up...........is the BAC trying to maintain a 750rpm idle. It sees the low rpms and then adjusts its duty cycle to let more air in.......rpms drive back up........BAC lowers it duty cycle to let less air in...........idle drops back down to 100rpm.......and an endless cycle happens.

Cause by the idle not being set right. Idle should be set per FSM to approx 750rpm. If that is done, then you won't have the endless cycling anymore. When you do set the idle, your supposed to install the initial set coupler. What that act does, is set the BAC's duty cycle to a SET value, so it won't be driving up/down as you set the idle using a screwdriver.

Then again, a improperly routed vacuum line. leaking vacuum line etc could be a problem also. Hard to say.

Hey, do this. Get the engine hot, and let it get into its cycling job. Now while it's doing the cycle job, pull the BAC's electrical plug off. I bet the engine dies when you do that .

 

Hmm.. I'll give it a shot this weekend guys, I'll let you know what happens! Thanks!

-Bart