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| DaleD | Another rough idle | ||
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Senior Guru
 
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My car is running pretty well, but once it warms up, the
idle seems to go low enough to cause it to idle rough. When cold it idles at 700. Once it heats up, it drops to 600, and will start to hunt down to 500. When it gets to that point, it starts chugging. Any ideas? |
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Posted on: 2009/7/9 18:40
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Whenever someone says "I'm not book smart, but I'm street smart", all I hear is "I'm not real smart, but I'm imaginary smart". |
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| TommyT-Bone | Re: Another rough idle | ||
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Chair-man of the bored
 
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Did you ohm the injectors? Seems to be popular lately.
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Posted on: 2009/7/9 18:43
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| DaleD | Re: Another rough idle | ||
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Senior Guru
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It's been a while, but I'll do that. Mine's an 87, so it's not as common a problem as it is on the 89s. But, anything you overlook will bite you in the a$$.
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Posted on: 2009/7/9 19:01
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Whenever someone says "I'm not book smart, but I'm street smart", all I hear is "I'm not real smart, but I'm imaginary smart". |
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| Matatk | Re: Another rough idle | ||
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Webmaster
 
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Did you start with the basics? Check the FP, injectors, reset IAC, check TPS, etc.
Matthew |
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Posted on: 2009/7/9 19:24
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| pianoguy | Re: Another rough idle | ||
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Guru Emeritus
 
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Yes, don't forget the etc. - I am still putzing with the etc. on my car. |
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Posted on: 2009/7/9 19:29
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1996 LT4 �Before you criticize someone, you should walk a mile in their shoes. That way when you criticize them, you are a mile away from them and you have their shoes.�- Jack Handey |
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| DaleD | Re: Another rough idle | ||
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Senior Guru
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Quote:
Actually, I started only with noticing the problem and posting here. Figured I'd come away with a plan after seeing the replies. My guess is the FP is unlikely. It was replaced last year and only has about 2k miles on it. Also, the car accelerates nicely. The rough idle seems to be a result of the idle speed being too low. I'm going to check the injectors this weekend. I'll have to research the IAC reset and TPS setting, those seem like they could be likely causes. |
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Posted on: 2009/7/9 19:41
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| josephf31 | Re: Another rough idle | ||
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Senior Guru
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Vacuum leaks can play havoc with idle smoothness; I recently replaced most of the old rubber hoses under the hood on my '91; easy and cheap... |
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Posted on: 2009/7/9 20:54
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| pianoguy | Re: Another rough idle | ||
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Guru Emeritus
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O2 sensors could be a factor, too - if they aren't reading correctly it can mess up your fuel mixture.
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Posted on: 2009/7/10 0:09
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1996 LT4 �Before you criticize someone, you should walk a mile in their shoes. That way when you criticize them, you are a mile away from them and you have their shoes.�- Jack Handey |
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| DaleD | Re: Another rough idle | ||
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Senior Guru
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O2 sensor was replaced 2 years ago, probably about 5k miles on it. (I only have one). Not quite sure how to diagnose that one?
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Posted on: 2009/7/10 0:42
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Whenever someone says "I'm not book smart, but I'm street smart", all I hear is "I'm not real smart, but I'm imaginary smart". |
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| Steve40th | Re: Another rough idle | ||
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Elite Guru
 
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I would seriously test the IAC /and clean it.
http://shbox.com/1/iac2.jpg |
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Posted on: 2009/7/14 7:27
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| DaleD | Re: Another rough idle | ||
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Does that diagram apply to an 87 TPI as well? |
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Posted on: 2009/7/14 13:42
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Whenever someone says "I'm not book smart, but I'm street smart", all I hear is "I'm not real smart, but I'm imaginary smart". |
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| CFI-EFI | Re: Another rough idle | ||
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Senior Guru
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With only these symptoms, it isn't fuel pressure, fuel pump, or fuel injectors. Vacuum leaks DO cause problems with the idle, but the additional air from a vacuum leak makes it idle faster, not slower. Resetting the IAC is only needed when installing or reinstalling the IAC. The IAC will self reset if the procedure isn't performed. It isn't a tune up or maintenance operation. The low idle speed indicates a lack of sufficient air. Because you report the idle speed changes as the engine warms up (as it should) it seems the IAC is working. You should be looking at why the engine isn't getting enough air for a proper idle speed. I would start by checking the IAC passage in the TB for a restriction, such as a carbon build up. RACE ON!!! |
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Posted on: 2009/7/14 15:07
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