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What is the cause of my idling problem?

Tiny
JOSHFAHRENHEIT
  • MEMBER
  • 1988 GMC VAN
  • 145,000 MILES
I have a 1988 GMC Vandura 2500 5.7 ltr V8. Here's my story: The van was slowly acting weird, strange idle, lack of power. I tried to leave a parking lot on Thanksgiving, and it just died and wouldn't start back up. I thought I had bad gas or something and had to get it towed. I put in Lucas gas treatment and put higher octane gas in it (about half a tank) and it seemed to be better. Now it's idling erratically again. Up real high then down real low and wants to die. Back and forth, up and down. I have to give it gas to keep from dying when the idle drops. What could it be? I saw a section on here about a vacuum leak causing a whistling sound. I have noticed the past month of a whistle sound that was not there before. Please help me, I already had to be towed on Thanksgiving and I'm very poor right now.
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Sunday, November 27th, 2011 AT 9:05 PM

10 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Clean out the idle air control valve and EGR/PCV valves and see what happens
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Sunday, November 27th, 2011 AT 9:13 PM
Tiny
JOSHFAHRENHEIT
  • MEMBER
  • 6 POSTS
Okay, will do. I'm not much of a mechanic. I'm trying to find where the idle air control valve is located, not coming up with much online.
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Sunday, November 27th, 2011 AT 9:52 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Its on the throttle body-you need a repair manual
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Sunday, November 27th, 2011 AT 10:26 PM
Tiny
JOSHFAHRENHEIT
  • MEMBER
  • 6 POSTS
I found it! Took it off and cleaned it with carb cleaner. The springs around it moved but the post (part with metal tip) didn't seem to move in and out. I'm not sure if it is supposed to or not. I put everything back together, and no real change in idle- still up and down. Onto the EGR/PCV valves I guess?
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Monday, November 28th, 2011 AT 12:31 AM
Tiny
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  • MECHANIC
  • 75,992 POSTS
When you turn key on the IACV should move if not its defective
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Monday, November 28th, 2011 AT 2:06 AM
Tiny
JOSHFAHRENHEIT
  • MEMBER
  • 6 POSTS
Okay. I turned the key and could see the IACV move in and out. Pretty cool :) So we can rule that out? I think I've located the EGR valve. Just remove it and clean? Thanks for all your help!
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Monday, November 28th, 2011 AT 10:13 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
You're welcomed
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Monday, November 28th, 2011 AT 10:31 PM
Tiny
JOSHFAHRENHEIT
  • MEMBER
  • 6 POSTS
One last question. The IACV did NOT move when the ignition key was in the "on" position. It only moves when I started the engine up. Is it defective?
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Tuesday, November 29th, 2011 AT 5:24 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Go to this link and understand how it works-https://www.2carpros.com/articles/how-a-idle-air-control-valve-works
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Tuesday, November 29th, 2011 AT 6:36 AM
Tiny
JOSHFAHRENHEIT
  • MEMBER
  • 6 POSTS
Well, I changed out the IACV, seemed to do better, then it was bad again. I took out the EGR- it seemed stuck, so I sprayed wd-40 and had it working smoothly. Neither seemed to fix my problem. It got worse and worse and finally stalled wouldn't start up again at all. I had to have it towed to a mechanic :( Any thoughts on what it could be? I sure hope I don't get ripped off.
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Wednesday, November 30th, 2011 AT 7:15 PM

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