Help pete good old fashion high idling 1500 rpm's
#1
01-14-2012, 03:26 PM
Help pete good old fashion high idling 1500 rpm's
ok 1994 3.4 147,000 miles auto. changed IAC to a new one and changed PVC. the car still revs at 1500 rpms. where are all the vacuums located, looks pretty clean on the throttle body and it opens and closes fine. what about the TPS??? HELP HELP WHAT ELSE!!!
#4
01-14-2012, 08:53 PM
Check all vacuum lines for leaks. There should be a sticker in the engine compartment. Using a scanner verify the that the coolant temp sensor (ECT) is reporting the proper temp to the PCM. The inside of the TB is factory coated with a gummy substance to ensure a tight seal when the throttle valve is closed. If the TB was cleaned you may have to adjust the stop screw to ensure a tight seal. All idle air should be provided by the IAC. To properly adjust the stop screw, make sure the TPS is properly installed and using a scanner adjust the stop screw so that the scanner shows a TPS angle of exactly 0.0%.
Verify that the voltage always returns to the same value at idle. The PCM will idle the engine at a normal speed when the TPS voltage returns to the learned base idle value. This is also called 0% throttle angle. If this throttle angle is 1% or more at idle, the PCM will assume the engine is actually off idle and raise the engine speed to prevent a closed throttle stall.
Note that another sensor using the same 5-volt reference as the TPS can momentarily glitch the reference voltage low. This will cause the TPS to send a lower base idle voltage to the PCM, which the PCM quickly records as the new learned base idle voltage. When the reference voltage returns to 5 volts, the base TPS signal voltage increases to its previous value. The PCM now interprets this as being off idle. This will cause the throttle angle to increase to 1% (or more) and idle the engine at a fast speed. 1. Monitor the throttle angle (or percent). It should always be 0% with a closed throttle.
If the throttle angle is not 0, sweep the Throttle Position Sensor (TPS) signal voltage output. Verify that the voltage always returns to the same value at idle.
Check for another sensor pulling the 5-volt reference low to the TPS. You will need a wiring diagram)
If TPS voltage always returns to the same value, but the throttle angle does not go back to 0, then the PCM is misinterpreting the information, probably due to the TPS not being to factory specs.
Verify that the voltage always returns to the same value at idle. The PCM will idle the engine at a normal speed when the TPS voltage returns to the learned base idle value. This is also called 0% throttle angle. If this throttle angle is 1% or more at idle, the PCM will assume the engine is actually off idle and raise the engine speed to prevent a closed throttle stall.
Note that another sensor using the same 5-volt reference as the TPS can momentarily glitch the reference voltage low. This will cause the TPS to send a lower base idle voltage to the PCM, which the PCM quickly records as the new learned base idle voltage. When the reference voltage returns to 5 volts, the base TPS signal voltage increases to its previous value. The PCM now interprets this as being off idle. This will cause the throttle angle to increase to 1% (or more) and idle the engine at a fast speed. 1. Monitor the throttle angle (or percent). It should always be 0% with a closed throttle.
If the throttle angle is not 0, sweep the Throttle Position Sensor (TPS) signal voltage output. Verify that the voltage always returns to the same value at idle.
Check for another sensor pulling the 5-volt reference low to the TPS. You will need a wiring diagram)
If TPS voltage always returns to the same value, but the throttle angle does not go back to 0, then the PCM is misinterpreting the information, probably due to the TPS not being to factory specs.
Last edited by z28pete; 01-14-2012 at 09:03 PM.
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