I was goin back to college today and while cruising around 70-80 mph my rpms would drop 500 then go back to normal. I noticed when i hit the gas it would drop, when i let off it would return to normal. No SES light. No other problems. It would come and go.Right before the 500 rpm drop it would fluctuate 100 rpm or so.

What is it?
Knock retard or ignition problem?

Thanks

Matt

 

Maybe it is torqueconverter clutch that is locking,and drops rpm's.Could be some misadjusment at swith that is at brakepedal assembly.

Jari

 

Thanks. When you say switch at the brake pedal, what switch are you talking about? Shouldnt the tcc lock up earlier? Its a '89 305 TPI in a '85 TA. The '85 harness and ecm is still used.

O yea, the speed remains basically the same. Also, there is cruise control, but the wires are cut at the turnsignal lever, and i unhookd the cable from the throttle.

Thanks,

Matt

 

It is switch that controls cruicecontrol vacuum signal and torque converter clutch supply voltage(+12v).You can also measure controlvoltage at aldl connector(pin A=ground, pin F=tcc solenoid).
There should be 12v between A and F when engine is running and brakepedal is not pressed.When you press brakepedal voltage should drop to zero.Then drive car steady speed say 50 mph,and look that voltagemeter,when tcc lock-ups voltage shold drop near zero (about 100mV).

Jari

 

Could the TPS be the problem? What about bad main bearings or rod bearings? Or tranny problem?

Just some ideas. I have my reasons for thinking these things may be slight possibilitys.

Thanks,

Matt

 

ttt