High Idle problem

GMC
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A79BIGBERTHA
  • MEMBER
  • 2 POSTS
1994 Camaro, automatic, 3.4 engine, 130,000 miles
When starting my camaro it idles at 2,000 rpm and slowly raises to 2,500 where it levels out indefinatley. The engine always runs smooth and I have just replaced the idle air control valve, intake air temperature sensor and all of the vacuum hoses. after installing all of this it seems to have no effect on the high idle problem. Please keep in mind this engine does not have a MAF sensor. Also, I have checked and cleaned the throttle valve and it closes tightly. Please tell me what else could be the problem... Thank you.[/b]
Feb 25, 2006 at 6:36 AM
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DAVID1984
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  • 7 POSTS
Have you tried you throttle position sensor, that could affect as well.
Feb 25, 2006 at 7:11 AM
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A79BIGBERTHA
  • MEMBER
  • 2 POSTS
Thanks for the suggestion. I replaced the TPS after you reccomended it, and it did help very slightly though. It is now idling between 2200 and 2300 RPM, which is still way too high. Does anyone have anymore suggestions on what to check next? Thank you for your help...
Mar 2, 2006 at 10:12 AM
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JDL
  • ✓Experienced Mechanic
  • 16,098 POSTS
If the vehicle is a speed density system, map only, A vacuum leak can cause the idle to go high.
Nov 22, 2010 at 1:20 PM
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Suggested Repair

On this MAP-only speed-density system, inspect for a vacuum leak, which can cause a sustained high idle. The IAC valve, IAT sensor, vacuum hoses, throttle plate, and TPS have already been addressed, with only a slight improvement after the TPS replacement.

Conversation Summary

A 1994 Camaro with a 3.4 engine idles at about 2000 RPM on startup and rises to about 2500 RPM, where it stays. The engine runs smoothly and has no MAF sensor. Replacing the idle air control valve, intake air temperature sensor, and vacuum hoses, plus cleaning the tightly closing throttle plate, did not fix it. Replacing the throttle position sensor lowered the idle only slightly to about 2200-2300 RPM. The expert advised that a vacuum leak can cause high idle on a MAP-only speed-density system.

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