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Old 07-31-2006, 07:28 PM   #1
gesingle
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1995 SL2
Default Fast Idle Problem Solved

Iíve seen several threads on the forum that sound similar to my 1995 Saturn SL2 problem, but none of the suggestions worked for me. When releasing the throttle during cruise, the engine maintains RPM for a second before decreasing power. When braking, it feels like I am fighting the engine. Coming to a stop, the idle remains high for a few seconds.

I cleaned the throttle body. That didnít help, so I replaced the Idle Air Control Valve (IAC), TPS, and ECTS. Still no improvement, and no vacuum leaks were apparent. I suspected the delay was caused by the IAC opening too far, behaving like a throttle and allowing too much air to enter the manifold. Releasing the throttle does not slow the engine until the IAC closes.

To verify this, I disconnected the wires from the IAC while the engine was idling. I then drove the car. Throttle response was instantóno more delay. CAUTION: If you try this, reconnect in the following sequence: Shut off engine. Disconnect battery. Reconnect wires. Reconnect battery. You may need to partially depress the accelerator when restarting. Disconnecting the battery causes the computer to forget the IAC settings and forces it to relearn.

According to the service manual, the PCM (computer) learns the proper IAC position and controls idle speed based on coolant temperature (ECTS), park/neutral switch status, vehicle speed, battery voltage, and A/C. All of these inputs were good, but what if manifold pressure is part of the speed calculation? I replaced the MAP sensor and disconnected/reconnected the battery to reset the IAC program. Problem solved! My Saturn now runs normally.

I hope my experience is helpful to others experiencing this problem.

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Old 07-31-2006, 08:02 PM   #2
RangerRuss
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2003 VUE 2.2L
Default Re: Fast Idle Problem Solved

Perseverance usually wins out. Does anyone know how to test a MAP sensor prior to buying all these parts?

Russ

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Old 07-31-2006, 10:34 PM   #3
gesingle
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1995 SL2
Default Re: Fast Idle Problem Solved

Quote:
Originally Posted by RangerRuss
Perseverance usually wins out. Does anyone know how to test a MAP sensor prior to buying all these parts?

Russ
In my case, the MAP sensor was working at least well enough so that the PCM did not give an error code. There was carbon buildup in the sensor's tube that may have restricted flow and slowed its response enough to fool the PCM.

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Old 08-01-2006, 02:28 AM   #4
Bigdaddy94sc2
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2006 ION-2 Sedan
2005 VUE 3.5L
Default Re: Fast Idle Problem Solved

You can check the voltage at idle. It should be between 1-1.5v at idle. Closer to 1 is normal, but as high as 1.5v is still acceptable.

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