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Discussion Starter #1
I hate to do it considering there are a few I found when searched, here's the deal.

95 XLT. 5.8L, Idle has progressively climbing on me. I went through the vacuum hoses today and could not find any apparent leaks, they were all in good shape, couldn't even find cracks in them. In park it's idling at 900-1000 RPMS.

Before I start throwing money at a problem I was hoping to get some ideas. I had read about the IAC valve, cleaning and replacing etc.. is there a way to test if that could be the culprit?
 

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Unplug it
 

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I had a similar problem once, it was the gasket between the upper and lower intake's that was pushed out, causing a massive vacuum leak.
 

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green ones make me horny
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IAC are not serviceable. test it first, and then go from there.
 

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Satyr of the Midwest
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I'd make sure the throttle isn't hanging open first by popping the throttle cable off the lever on the throttle body.
 

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Discussion Starter #7
I popped the cables off and there was no change, I then unplugged the IAC Valve and also no change. I have never removed the IAC or done anything to it so I don't know that the gasket could have failed, but even if it had i imagine there would have been some change to the idle when it was unplugged... I had also considered the idle adjustment (though I know it couldn't have been moved on me) and it was also set fine, i backed the bolt off the striker plate and it just backed away from it not moving the throttle at all so i just put it back where it was.
 

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Satyr of the Midwest
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Have you checked TP voltage? It shouldn't make a difference, but I'd test it anyway. Should be in the 0.80V to 0.95V range.

After that, I'd start taking off vacuum lines and plugging ports, just to completely eliminate any connected parts as potential vacuum leaks. The ones where the vacuum reservoir attached to the HVAC box leak are fun to pinpoint.
 

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green ones make me horny
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I popped the cables off and there was no change, I then unplugged the IAC Valve and also no change. I have never removed the IAC or done anything to it so I don't know that the gasket could have failed, but even if it had i imagine there would have been some change to the idle when it was unplugged... I had also considered the idle adjustment (though I know it couldn't have been moved on me) and it was also set fine, i backed the bolt off the striker plate and it just backed away from it not moving the throttle at all so i just put it back where it was.
well test your IAC according to haynes manual. After that take it off of the throttle body and plug it in. have someone turn the key on, no start, and see if the plunger inside is moving. if not replace it. the truck should damn near die when you disco the IAC valve
 

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Discussion Starter #10
well test your IAC according to haynes manual. After that take it off of the throttle body and plug it in. have someone turn the key on, no start, and see if the plunger inside is moving. if not replace it. the truck should damn near die when you disco the IAC valve
I will read up and test it and get back to ya'll with the results. Like i said there wasn't any change in the idle when i unplugged it, aside from my doing it you wouldn't have even known that it had been unplugged.


Kinda funny, i had put the dust cover back on the TB yesterday and went to run an errand, well i backed out of my drive way and put it in park only to find that there was no reaction when i hit the throttle. So now I'm out in the middle of my street hooking the throttle cables back up :rofl: Fortunately i have some good neighbors...
 

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Discussion Starter #11
I haven't found anyone to give me a hand turning the engine over while i look at the valve. I did however test it with my ohm meter and it read anywhere from 10.8 to 11.2 according to the book that's still good. It said that if the reading were not 7-13 then to replace it.
 

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Discussion Starter #12
Have you checked TP voltage? It shouldn't make a difference, but I'd test it anyway. Should be in the 0.80V to 0.95V range.

After that, I'd start taking off vacuum lines and plugging ports, just to completely eliminate any connected parts as potential vacuum leaks. The ones where the vacuum reservoir attached to the HVAC box leak are fun to pinpoint.

Having not run into this kind of problem before i'm not sure how to test the TP Voltage. If you could give me a run down on how to do that i would really appreciate it. In the meantime i will start blocking off vacuum lines.
 

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green ones make me horny
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TPS Testing is in the haynes manual as well
 

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Satyr of the Midwest
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:stupid Basically, grab your volt meter and a couple of hat pins, and start probing.

Read this page for further information: http://www.supermotors.net/registry/media/173616

There should've been a definite engine speed change when you unplugged the IAC, though. I must've glanced over that part of your post earlier. That's further evidence of a vacuum leak somewhere, or a sticking (not fully-closing) throttle.
 

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Discussion Starter #15
:stupid Basically, grab your volt meter and a couple of hat pins, and start probing.

Read this page for further information: http://www.supermotors.net/registry/media/173616

There should've been a definite engine speed change when you unplugged the IAC, though. I must've glanced over that part of your post earlier. That's further evidence of a vacuum leak somewhere, or a sticking (not fully-closing) throttle.
Yeah i had read the TP sensor testing and was a little confused by it. At one point it tells you that if the resistance readings are about equal to the values in the table then the sensor is fine. Now that part i understand, what i missed was the table to compare the numbers in. There is no table. :banghead

Regardless, I'm leaning back towards the vacuum leak also, i replaced the TP sensor a couple years ago. I'm just going to keep pulling and plugging lines to see where i might have a leak. My father suggested spraying starting fluid around where i think the leak may be and if the engine revs up then it's a good chance i found my leak. I haven't done that, i have just been feeling around the hoses, looking for wear, stuff like that so far.
 

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Have you clean your throttle body? Have you cleaned your IAC?
 

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Discussion Starter #17
Have you clean your throttle body? Have you cleaned your IAC?
Reading through the posts on here it seems that cleaning the IAC isnt the best idea considering usually soon after it will need replaced. I havent ruled the IAC out yet, i just need another set of hands to turn the key while i watch the inside of it. Nothing happens when i unplug it and that's why i am still considering it. As far as cleaning the throttle body, it has not been done , but there isnt a whole lot of gunk or anything around/on it. regardless it is something i will try also.

I have orders to report to FT. Eustis in VA. for the next couple weeks so i may not get to it right away but i will bump this thread when i get back and get a chance to dedicate a day to it.
 

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Have you checked TP voltage? It shouldn't make a difference, but I'd test it anyway. Should be in the 0.80V to 0.95V range.

After that, I'd start taking off vacuum lines and plugging ports, just to completely eliminate any connected parts as potential vacuum leaks. The ones where the vacuum reservoir attached to the HVAC box leak are fun to pinpoint.
I had this problem as well, turned out to be the Throttle Position Sensor. Replaced it and everything was good!
 

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Satyr of the Midwest
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Cool. Hopefully I'll have the rest of my crops planted by then. :thumbup

One off-the-wall troubleshooting technique I've thought of would be to remove the IAC, and then plug the side leading to the plenum (with what, I don't know yet lol). That way, you'd be assured that the only air entering the manifold would be from a vacuum leak or around the throttle blades. I'd initially thought that using your thumb would work, but then the safety issues started gnawing at that idea. :rofl:
 

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Any updates on a fix yet . I am having the same issue with my 95 and have already replaced the IAC with no luck . My truck will idle all the way to 2k in nuetral after driving but the strange part is on some very warm days it idles fine . I unpluged the connector and vac line to my map sensor and it idled down so I am looking at that as a posible problem now .
 
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