Hey guys, I currently have an '88 fc n/a 5 speed. Whenever I let go of the gas, no matter the speed or rpm, the car seems to "bog" or "chug", kind of a minor jump back and forth. It will only stop if I either push in the clutch or the gas pedal. The car runs perfectly but this is definitely annoying. Any response would be greatly appreciated.

 

Sounds like excessive gear lash or play in the driveline, i.e. transmission, u-joints, differential, or half-shafts.

But, if you think its the engine doing it, there is a procedure in the FSM to diagnose problems in rough running under decelleration. The ECU reduces the fuel during decelleration to keep it lean, and the AAV adds air for the same reason. If either of those are not functioning correctly, or are overdoing it (too lean) it can cause problems in decelleration.

If you put the clutch in and rev it up does it falter on decelleration? If not, it is not likely the engine management.

 

Try resetting the Throttle Position Sensor (TPS)

 

If I push in the clutch or give it gas, decelleration is not a problem, only when in gear. How do I reset the TPS?

 

A lot of times people will just reply with the right key words and expect you to search for yourself or look it up in the FSM. In this case there are a lot of threads without the actual procedure, so here's a link to a good walkthrough.
http://www.fc3spro.com/TECH/HOWTO/TPS/tps.html
If you get the same behavior when you are barely on the throttle or cruising on the highway, this will probalby help. Good luck.

 

Thanks guys for your input. I reset the TPS and now the cars drives much better. The restriction wasn't much (1.7 ohms) but it damn sure made a big difference. Thanks again.

 

The jpg attached is out of the series five manual but is the same for the series four cars.

Drive along and let off the pedal just a touch and the ECU cuts fuel to the FRONT rotors. Then let off the pedal all the way.....FRONT and REAR both get cut by the ECU.

Stay off the pedal and let the rpms drop to approx 1300rpm and both front and rear primarys come back online.

IT done for DRIVABILITY. So the car won't bump and jerk when decelerating. It depends heavily on the TPS being set right among other things.

 

wow! so that's what's going on! I always thought my TPS wasn't set quite right or something.