Trying to fix an high idle issue - TPS maybe?
01-24-2014, 02:42 PM
#16
Here is a little info on how the ISV works that might help.
The ISV does not have a 'standard' position like other systems. Many idle air valves default to closed when power is removed. The 944 ISV stays wherever it is until it receives a new signal. The ecu doe not really know how much the ISV is opened or closed, it only reacts to the RPM and tried to open or close the ISV to get to the right RPM. If the ISV is sticking (and it can get gummed up) RPMs may hang either low or high, if there is an issue with the wiring the same thing can happen.
All that being said if the ECU does not see an idle position signal from the TPS it won't try and stay at idle speeds.
The ISV does not have a 'standard' position like other systems. Many idle air valves default to closed when power is removed. The 944 ISV stays wherever it is until it receives a new signal. The ecu doe not really know how much the ISV is opened or closed, it only reacts to the RPM and tried to open or close the ISV to get to the right RPM. If the ISV is sticking (and it can get gummed up) RPMs may hang either low or high, if there is an issue with the wiring the same thing can happen.
All that being said if the ECU does not see an idle position signal from the TPS it won't try and stay at idle speeds.
The TPS clicks and works normally otherwise. Unless the car has sat for 10 minutes warm and it is restarted. Then it hangs around 1200 RPM idle and when shifting the revs hang. After another 15 minutes of driving the car comes back to normal once again.
01-24-2014, 09:38 PM
#17
Rennlist Member
My old TPS clicked at idle setting and when I removed it and bench tested it with a ohmmeter (cold) it was fine. It only appeared to malfunction at high underhood temperatures. I tended to have the high idle condition after a hot restart or if stuck in summertime stop and go traffic. Its an easy swap so perhaps its worth a try if you have eliminated the other possibilities.
