Disconnect TPS, engine runs like normal.


I have been trying for a while now to fix a low idle issue on my 91 Ls AT. The problem is when I put it into drive or reverse, the idle drops below 750 and the car then vibrates from the low idle, gets worse the more accessories I turn on esp AC.

I have replaced the IACV valve, coolant temp sensor for the ECU, pcv valve, fuel filter, plugs.

The other day I tested the TPS sensor, voltages were way out of range and had a few dead spots, however when I am driving there are no dead spots or hesitation at all.

So then I disconnected the TPS sensor and started up the car, ran exactly how it does with it plugged in. I am a little puzzled by this, every thread I read where the tps sensor was bad say the car will either die or hesitate. mine does neither except idle low.

No CEL’s with the tps plugged in, is it possible that the ECU is just going into a closed loop mode and not using the TPS sensor? is this even possible? how can I drive like normal without a TPS?


Bump, anyone have any ideas? I changed the O2 sensor to see if that was causing a closed loop only symptom but it’s still doing the same thing. Completely stumped on this issue, any help is appreciated.

My car is currentlt doing the same thing. Were you ever able to figure out if the TPS was the issue?

Sounds pretty normal, for an automatic.