I have been working to get all the bugs out of my 89 n/a street-port daily driver and I have one lingering problem. whenever I press the clutch in while idling the engine continuously revs up and then settles back down then revs up and settles back down. I have tuned the engine by adjusting the timing and TPS to factory spec. I had to bump up the idle to 900 rpms to keep it from doing the same thing in neutral.
has anyone encountered this problem and know a solution? Thanks.

 

I did, bad TPS. Installed a new one no problems.

 

figured out it was the thermo wax. tried adjusting the thermo wax using ice water and boiling water to factory specs with little success. then i decided to completely remove the thermo wax from the equation by a using a stand off about 4 mm inside by 20 mm long slipped over the adjusting screw, completely eliminating the chance the fast idle cam would touch the throttle linkage.

 

One of my friends had exactly the same problem : figured out it was related to the transmission so he changed one of the switch from the transmission and his problem was solved.

Look for neutral switch or clutch switch at F1 (04A_Fuel_and_Emission_control_systems_non_turbo) p.85-86 in the FSM

Hope it helps !