High Idle at Cold Temperatures 3000 RPM - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 12-02-2009, 05:21 PM   #1
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Default High Idle at Cold Temperatures 3000 RPM

When it'* been bitter cold here (0 degrees F or below) The first thing in the morning when I start my 1996 Bonneville I experience a high idle. It starts out at 1500 rpm and climbs to 3000 RPM. After the car warms up and I put it into gear and drive it for 10 seconds, the idle returns to normal (in neutral and in gear) It'* a new engine, when I replaced the motor, I replaced all the sensors on the manifold. This has just come up and the motor doesn't even have 25,000 miles on it. Any suggestions? Also the check engine light came on, I got a bank 2 O2 sensor code, but since has been cleared and the MAP sensor keeps coming up, the MAP sensor is good. Could the O2 sensor be the cause of this high idle problem? Oh and the Check Engine light doesn't come on if it is hot outside, only under 50 degrees will it come on. I've replaced everything pictured below.
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Old 12-02-2009, 05:51 PM   #2
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Please only start one thread for one issue
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Old 12-02-2009, 06:34 PM   #3
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You will want to check your intake air temp sensor. You can also check your Idle Air control.
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Old 12-02-2009, 10:44 PM   #4
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I'm with Dan on the IAC valve or maybe a dirty throttle body.
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Old 12-07-2009, 04:52 PM   #5
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Ok, so I took the Throttle body off and cleaned it, everything looked good, butterfly closed all the way. I replaced the IAC, Throttle positioning sensor, and Map Sensor. Got the car to start up cold and it started idling at 2500 RPM. I hooked the car up to a Master Tech computer and went and tried to manually control the IAC. It wouldn't respond. I tried bringing the RPM'* down to 650 and it continued to idle at 2500 RPM. Once the car got warm, the idle dropped and then I could control the idle with the computer. Another thing I thought was strange was the voltage going to the IAC . I checked the plug and it registered 10 Volts, all the other sensors are 5 volts. I couldn't find any specs for the voltage, but I thought that was kind of high. Sorry about the multiple posts, I accidentally put the first post in the wrong category.

Does anyone have any suggestions or similar problems? I was working on it yesterday, I put a new rack in the car, found out there were 3 different racks in 96, apparently mine has Magnasteer which so happens to be the most expensive rack option 225 bucks;ouch!

Note: the Check engine light does not throw any codes either.
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Old 12-07-2009, 05:16 PM   #6
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The only codes it throws are the ones for the sensor if you unplug it while the car is running.
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Old 12-07-2009, 05:27 PM   #7
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Also the computer when hooked up to the car says all the related sensors are operating properly and within range. I still can't for the life of me understand why the car wouldn't let me manually control the IAC when it was idling at 2500 RPM.
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Old 12-07-2009, 07:48 PM   #8
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I think there are different tables for warmup idle based on coolant temp as well as different fuel ratios, it might not let you interrupt that
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Old 12-07-2009, 07:52 PM   #9
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The only other thing I can think of is the ECT, Engine coolant temp. The PCM sets the idle according to the coolant temp.
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