I have a 1999 Chevrolet Camaro with a 5.7 liter engine and a manual transmission.

It recently started idling high but only when coasting. If I slow down because of a stop sign or whatever and hit the clutch, it'll idle from 1400-1800 rpm. It will do this in neutral as well. The idle stays there until I come to a stop. It's fine while sitting still, it's just while coasting, even at slow speeds.

I had a check engine light on but unhooked the battery and when I reattached it the check engine light did not come back on.

  • 1
    My 03 Acura RSX-S does this.... I assume it's because of the brake booster or something though now that I think about it this is an odd happening... May 4, 2015 at 22:17
  • Do you have any way to read the what the throttle position sensor (TPS) is reading at any given time? A scanner with live data could be an invaluable diagnostic tool right now. May 4, 2015 at 22:26
  • 1
    The usual culprits are the throttle position sensor or idle control valve. Occasionally it can be more complicated, like bad cam timing. May 5, 2015 at 6:59

2 Answers 2


Sounds like the IAC (Idle Air Control) valve/sensor is faulty. The IAC is a small piston that moves in/out and regulates how much air goes through it to control the idle speed. Your issue seems to be that the IAC is getting stuck in the open position (due to wear or it being dirty) and then working again once a full stop happens.

Get some throttle body cleaner and spray it in. If that doesn't fix it the part is pretty cheap. Like $20. You can replace it yourself. Its the one in the bottom. Remove two bolts and replace. That's it.

IAC location


The Problem is caused by the throttle Position sensor or the linkage.

Its Quite common for an old vehicle to develop this issue , take it to a mechanic and tell him exactly the issue.

Old mechanical cars tend to develop this issue due to weakening of the accelerator linkage. Will not cost much to repair.

  • Nope But, I had the same issue and took it to the mechanic , was extremely cheap to fix(like around $12, I don't live in the US so converting) and I feel he should do the same and he might not mess up his engine since it involves opening the cylinder head.
    – Shobin P
    May 6, 2015 at 7:29
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    I think you may have your terms crossed here. If it involved getting the cylinder head opened, it would cost way more than $12 ... you couldn't even buy a head gasket for his car for $12. Hopefully you are just misspeaking. Jun 20, 2015 at 23:47
  • @Anarach you would have to add a 0 to the end of your estimate, and probably double it. Dec 2, 2015 at 17:32

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