: Gas Pedal Tapping When Engine Shut's Off



ktills45
06-30-05, 08:18 PM
94STS, when the car shuts off, there's a tapping transmitted through the gas pedal which lasts about 20 seconds. Something to do with the throttle linkage, obviously.

Anyone have an idea what it might be?

Ranger
06-30-05, 10:30 PM
ISC motor needs replacing. Simple DIY job. Do a search for ISC or ISC motor. Lots of info.

BeelzeBob
07-01-05, 12:27 AM
The tapping is caused by the idle speed control motor.

The question is...did this just start all of a sudden or has it done this for a long time...??

If it just started then likely the ISC motor is failing and simply needs to be replaced.

If there is a long history of this then possibly the idle speed control motor is simply misadjusted. If the plunger on the idle speed control motor is too short then it will rachet trying to extend at key off and cause the tapping that you hear.

If you search using "idle speed control motor" in the archives there is a lot of information already available on diagnosing it.

For a quick check, open the hood with the enigne iding and hold the throttle lever open slightly to elevate the RPM to about 2500-3000 RPM. Simultaneously depress the plunger of the idle speed control motor with your finger. It should start retracting and continue retracting until it stops. Freeze it in this position by disconnecting the wiring connector to the idle speed control motor. Release the throttle lever and allow it to return to idle. The engine should idle very slowly (450-500 RPM) and there should be about 0.030 inch gap between the end of the plunger and the throttle lever. If the gap is more than that adjust the idle speed control motor plunger by turning it counterclockwise to unscrew it so as to lengthen it and reduce the clearance until you get it to 0.030 inch. Reconnect the wiring connector and cycle the key off and on several times. If this corrects the problem the ISC motor plunger just needed to be adjusted.

If the plunger will not retract or retracts roughly making noise or rachets like you describe then the motor is failed and needs to be replaced.

ktills45
07-01-05, 07:39 AM
I just heard this yesterday for the first time. I'm guessing that it's not mis adjusted, and that it's starting to fail. Thanks for the input all, I'll be taking care of this soon.

BeelzeBob
07-01-05, 03:12 PM
I just heard this yesterday for the first time. I'm guessing that it's not mis adjusted, and that it's starting to fail. Thanks for the input all, I'll be taking care of this soon.

When you install the new one adjust per the procedure above. Fully retract the plunger, check the idle RPM to make sure the engine idles down very low to 450-500 and adjust the plunger for a .030 gap.