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Revs up when coming to a stop, Code 24

Tiny
JOECOOLAMI
  • MEMBER
  • 1988 PONTIAC FIERO
  • 2.8L
  • V6
  • 2WD
  • MANUAL
  • 223,000 MILES
Here is the issue: The car listed above Formula model, starts up fine, idles fine (900 rpm's warm). But when driving after it warms up, if I am in neutral coming to a stop or if I push the clutch in to shift gears, it revs up to about 2,000 rpm's and stays there for a bit. It usually triggering a Code 24, but it will slowly start to come back down after a little bit. I also noticed that when below 2,000 rpm's, the vehicle will accelerate slowly with my foot off the gas. I checked again for vacuum leaks, but could not find any, and I have just replaced my EGR tube. My best guess is the throttle position sensor is going bad or poorly adjusted. Am I right or is there something else I should be looking for?
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Sunday, April 22nd, 2018 AT 7:11 PM

5 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning.

The most common issue for this is the idle air control on the throttle body. Remove it and clean the passage of all carbon. Usually carbons up and the valve sticks.

I attached a picture below to show you the location of the idle air control.

Roy
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Monday, April 23rd, 2018 AT 5:38 AM
Tiny
JOECOOLAMI
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  • 3 POSTS
Roy, thanks for the response. I just have one quick question. What should I use to clean out the IAC valve passage? I have some throttle body cleaner, but am concerned it might harm the IAC valve itself after reinstallation.
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Monday, April 23rd, 2018 AT 3:36 PM
Tiny
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  • MECHANIC
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I use 2+2 carburetor cleaner and a small wire brush that can get into the small areas.

Roy
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Monday, April 23rd, 2018 AT 4:23 PM
Tiny
JOECOOLAMI
  • MEMBER
  • 3 POSTS
Roy, I, and on behalf of my beloved Fiero, would like to extend our gratitude to you for you assistance. Even though the IAC valve was new, there was carbon buildup in the passage that was causing it to get stuck. I was not able to get in there with a wire brush like you said, as I purchased brushes too big, bit I did manage to scrape off a lot of residue with the help of some cleaner and a paper towel wrapped around my pinkie. Should issue arise, I will get the proper brush to give it a thorough cleaning. Took my car out for its first real drive and it drove magnificently! Thanks again!
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Tuesday, April 24th, 2018 AT 4:16 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
You are welcome. Glad to help. Thanks for visiting our site.

Roy
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Tuesday, April 24th, 2018 AT 4:22 PM

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