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2002 Cadillac High Idle Speed

CADILLAC
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SICKCADDY
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  • 2 POSTS
2002 Cadillac - standard NorthStar - 225K miles - on a level road, without cruise or accelerator pressure, vehicle will acellerate to and hold about 60 MPH. Shifting to Neutral allows RPM to increase and hold steady at between 2,400 and 2,600 RPM until it runs out of gas (for you guys who ask How Long?) or until the vehicle comes to a complete stop. After complete stop, takes about 3 seconds to begin a gradual (5 seconds) reduction in idle speed to 1,400 to 1,600 RPM. Same problem occurs anytime engine is at normal operating temperature. Replaced all sensors called for in error codes. Cleaned throttle body. I am not a mechanic, but I believe this is not operator caused stupidity like a sticky accelerator. It is in the computer controlled idle (fuel) system somewhere. Two different shade tree mechanics who charge like Cadillac technicians tried but failed to fix it. THANK YOU.
Jan 28, 2007 at 1:10 PM
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2CARPRO JACK
  • ✓Experienced Mechanic
  • 11,533 POSTS
I asume th eerror codes called for; TPS, MAF, IAC?
Need to start by using a meter to check for the 5 volt reference at all of these sensors, no vacuum leaks? If one sensor is shorted it can mess with the reference voltage and everything will be out of whack
Jan 28, 2007 at 11:23 PM
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SICKCADDY
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THANK YOU. Those things make sense to me. I feel like a "blonde" on the vacuum leak. I never even thought of that, so I will check that first. :oops:
Jan 29, 2007 at 12:06 AM

Suggested Repair

Check for vacuum leaks first. Then use a meter to verify the 5-volt reference at the TPS, MAF, and IAC sensors, since a shorted sensor can pull down the reference voltage and cause a high idle.

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Conversation Summary

A 2002 Cadillac with a Northstar engine and about 225,000 miles holds a high idle and can accelerate to about 60 mph without throttle input. In neutral, RPM stays around 2,400-2,600 until the vehicle fully stops, then slowly drops to about 1,400-1,600. Sensors indicated by codes were replaced and the throttle body was cleaned without success. The expert advised checking vacuum leaks and the 5-volt reference at the TPS, MAF, and IAC, noting that one shorted sensor can disrupt the shared reference voltage.

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