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  #16  
Old 08-13-2011, 08:15 PM
webster426 webster426 is offline
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Default Re: IAC Trouble

Pep Boys and autozone should check it for you. I would check the alternator and replace the IAC.....they arent that expensive.
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  #17  
Old 08-14-2011, 08:17 AM
propilot908 propilot908 is offline
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Default Re: IAC Trouble

already tried replaceing iac valve didnt help my problem
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  #18  
Old 08-14-2011, 08:32 AM
webster426 webster426 is offline
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Default Re: IAC Trouble

Get the alternator checked out and report back...
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  #19  
Old 08-14-2011, 08:36 AM
FireRanger FireRanger is offline
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Default Re: IAC Trouble

The voltage is going up and down because the RPM is dropping below a point where the alternator can generate power to keep up with the load placed on it. The RPM drop is causing the lower voltage, not the other way around. This is normal behavior of an alternator. The engine RPM would not change if the alternator was intermittently failing.

Your alternator is probably perfectly fine.
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  #20  
Old 08-14-2011, 09:15 AM
webster426 webster426 is offline
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Default Re: IAC Trouble

When the vehicle is drawing more power....i.e. the A/C is on etc., it will effect RPMs due to the power draw of the alternator. I would check the alternator.....
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  #21  
Old 08-14-2011, 09:34 AM
FireRanger FireRanger is offline
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Default Re: IAC Trouble

Nope. The RPM increases with the AC because of the mechanical load of the compressor on the engine. The computer brings the idle RPM up using the IAC to compensate for the mechanical load and provide additional power to the AC compressor. This has absolutely nothing to do with this situation.

Furthermore, the idle RPM does not increase or decrease with electrical load. Increasing electrical load on the alternator would increase the mechanical load on the engine spinning the alternator and IAC would vary throttle to maintain normal RPM. The RPM does not change. And there is nothing that would initiate any change in RPM either.

So once again, this is not an alternator problem and never was.
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  #22  
Old 08-14-2011, 11:49 AM
webster426 webster426 is offline
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Default Re: IAC Trouble

Quote:
Originally Posted by FireRanger View Post
Nope. The RPM increases with the AC because of the mechanical load of the compressor on the engine. The computer brings the idle RPM up using the IAC to compensate for the mechanical load and provide additional power to the AC compressor. This has absolutely nothing to do with this situation.

Furthermore, the idle RPM does not increase or decrease with electrical load. Increasing electrical load on the alternator would increase the mechanical load on the engine spinning the alternator and IAC would vary throttle to maintain normal RPM. The RPM does not change. And there is nothing that would initiate any change in RPM either.

So once again, this is not an alternator problem and never was.
I know all of this....but google "alternator causing rough idle"! There is plenty of evidence that supports my opinion. Furthermore, I am trying to help this guy out just like you are and I know the alternator CAN effect the vehicle at idle. Do some research and think outside of the box.....a bad alternator will cause ALL of the symptoms the OP described.

GET THE ALTERNATOR CHECKED! That is my two cents....take it or leave it. You can also try disconnecting the alternator while the vehicle is running and that will further eliminate or pinpoint the alternator as the issue. If you have a voltometer, check the battery terminals while the vehicle is idling AND while it is revved up. This should also help in my analysis...

----------

One more thing FireRanger.....you have not provided any solutions to his problem so why are you even in this thread? It appears you are only on here to disprove my solution which is definately plausible.
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  #23  
Old 08-14-2011, 11:59 AM
FireRanger FireRanger is offline
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Default Re: IAC Trouble

Quote:
Originally Posted by webster426 View Post
....take it or leave it. You can also try disconnecting the alternator while the vehicle is running and that will further eliminate or pinpoint the alternator as the issue.
This is evidence enough why your input should be ignored. That's the worst thing you could do and should never ever be done.

If I had a better idea than others that have already posted, I would have already suggested it. What I have done instead, is try to not make him waste his time. Or in the case of your latest suggestion, prevent him from frying something much more expensive. Your failing to look at the big picture of ALL the symptoms and just focusing on one of them.
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  #24  
Old 08-14-2011, 01:01 PM
webster426 webster426 is offline
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Default Re: IAC Trouble

LOL....whatever dude. Running on a diminished or worthless alternator is way worse then pulling the plug for a few seconds to see if the vehicle idles normally. Secondly, he wouldn't be "Frying" anything because he would be LOSING power, not gaining any. What you are implying is that any time an alternator goes bad you risk ruining "something expensive".

This post is not about you and me anyway, it is for the OP to decide and their is nothing wrong with my input.
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  #25  
Old 08-14-2011, 01:06 PM
FireRanger FireRanger is offline
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Default Re: IAC Trouble

Whatever you say pal. That's not how it works. I hope he chooses wisely in his troubleshooting efforts.
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How to: Aux light wiring, relays, & fuses
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Info: HID Projectors
How To: NO HEAT Troubleshooting Guide

Last edited by FireRanger; 08-14-2011 at 01:14 PM.
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  #26  
Old 08-22-2011, 07:01 AM
propilot908 propilot908 is offline
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Default Re: IAC Trouble

alright a while back a guy at autozone said to me when your truck is running unplug the iac valve so i tried it the truck did not stall out or anything in fact it idled at a steady 1000 rpm . so i went back to him saying what i said above and he said try changing you iac so i did and that did nothing for me. i mean the truck started much nicer with the new iac put it still did the up and down idle. i might have already explained this but not sure. I'm no sure what else i can do i mean its not hurting the performance of the truck its just annoying should i even worry about or just leave it. because i could end doing more harm then good after all its not likes it a new car so if anyone has any good ideas that be great
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  #27  
Old 08-22-2011, 08:30 AM
FireRanger FireRanger is offline
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Default Re: IAC Trouble

Remove and clean the throttle body too. Make sure the plate is close all the way and not all crudded up. I doubt this will help anything, kind of drawing at straws.\

Also, disconnect the battery for about 10 minutes to force it to relearn it's idle program. Also, where are you with the normal tune-up items like plugs, wires, etc?
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How to: Aux light wiring, relays, & fuses
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How To: NO HEAT Troubleshooting Guide
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  #28  
Old 08-22-2011, 09:51 AM
propilot908 propilot908 is offline
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Default Re: IAC Trouble

alright a while back a guy at autozone said to me when your truck is running unplug the iac valve so i tried it the truck did not stall out or anything in fact it idled at a steady 1000 rpm . so i went back to him saying what i said above and he said try changing you iac so i did and that did nothing for me. i mean the truck started much nicer with the new iac put it still did the up and down idle. i might have already explained this but not sure. I'm no sure what else i can do i mean its not hurting the performance of the truck its just annoying should i even worry about or just leave it. because i could end doing more harm then good after all its not likes it a new car so if anyone has any good ideas that be great
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  #29  
Old 08-22-2011, 12:49 PM
FireRanger FireRanger is offline
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Default Re: IAC Trouble

I think you pushed the wrong button.....
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How to: Aux light wiring, relays, & fuses
Info: 300+ intake threads here on FRF
Info: HID Projectors
How To: NO HEAT Troubleshooting Guide
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  #30  
Old 08-22-2011, 10:12 PM
bassmaster bassmaster is offline
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Default Re: IAC Trouble

So did you ever check the vacuum lines as i suggested 2 weeks ago? JW. an airleak into the UIM would negate the IAC causing it and possibly the MAF(depending on where said leak would be) to be bypassed.causing the 02 sensors to compensate for the "lean condition" Just a suggestion.especially if you have a 98-2000 with vacuum hubs.there are plenty of places for rotted vacuum lines.
oops saw you have a 96' still look for vacuum leaks. The only time i've seen an engine idle with the IAC unplugged is if there is air coming elsewhere(vacuum leak)
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Last edited by bassmaster; 08-22-2011 at 10:14 PM.
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