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Old 03-06-2011, 10:50 AM   #1
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Default Idle Air Control (IAC) Valve?

Well, I was driving this morning into the city, and after about 20 mins circling around for a parking spot, my jeep stalled out on me...at first, thought it was something either fuel or spark related...so double checked my spark plug wires and the wires on the cap and they were all on there properly. I kept trying to crank the motor and it would crank, but wouldn't start.

So after waiting about 20-25 mins, I gave it another shot and the Jeep started right up. Everything seemed normal, all the gauges were okay, no check engine lights and it was idling rock steady...so I continue to look for a parking spot and about about another 15-20 mins (yes, parking in the city on a Sunday morning can be difficult before a race - NYRR race - running) the Jeep stalls out again. By this time, the race start has passed so I said eff it...just going to head back home because I was more worried about getting home than anything else, plus I didn't really want to call a tow truck.

So I figure if I wait another 15-20 mins it would start up again, and surely it did. Drove about 45 mins on the highway with no hiccups and made it home with no stalling issues either.

So basically I think it's the IAC valve...should I replace it with a new one or just clean it and it'll be just as good? If it's not the IAC valve, where else should I look?

Thanks.

/rant
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Old 03-06-2011, 10:58 AM   #2
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Well, I was driving this morning into the city, and after about 20 mins circling around for a parking spot, my jeep stalled out on me...at first, thought it was something either fuel or spark related...so double checked my spark plug wires and the wires on the cap and they were all on there properly. I kept trying to crank the motor and it would crank, but wouldn't start.

So after waiting about 20-25 mins, I gave it another shot and the Jeep started right up. Everything seemed normal, all the gauges were okay, no check engine lights and it was idling rock steady...so I continue to look for a parking spot and about about another 15-20 mins (yes, parking in the city on a Sunday morning can be difficult before a race - NYRR race - running) the Jeep stalls out again. By this time, the race start has passed so I said eff it...just going to head back home because I was more worried about getting home than anything else, plus I didn't really want to call a tow truck.

So I figure if I wait another 15-20 mins it would start up again, and surely it did. Drove about 45 mins on the highway with no hiccups and made it home with no stalling issues either.

So basically I think it's the IAC valve...should I replace it with a new one or just clean it and it'll be just as good? If it's not the IAC valve, where else should I look?

Thanks.

/rant
When does it stall? Does it occur only when when you lift off the pedal?

Your description leads me to believe that your throttle-body (and IAC, etc.) just needs a good cleaning...
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Old 03-06-2011, 11:03 AM   #3
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When does it stall? Does it occur only when when you lift off the pedal?

Your description leads me to believe that your throttle-body (and IAC, etc.) just needs a good cleaning...

It happened both times while in an intersection (thankfully there was very little traffic). So I'm guessing it's when I lift off the brake (from a stop) then apply the gas. Weird thing was, when I was almost home, it didn't happen again while I was going thru the smaller side streets and stop signs.
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Old 03-06-2011, 11:06 AM   #4
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It wouldnt hurt to clean it (IAC), possibly fuel pump, dying CPS could be many things. Also have codes scanned even though no CEL is on it may have a cose stored.
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Old 03-06-2011, 11:14 AM   #5
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I wouldn't be too quick to indict the CPS yet (even though I agree it can cause weird behavior) and I agree that a stored code might be found if you do the scan. Good smooth idle, the fact that it restarts and there's still no CEL makes me think it's at the throttle body - possibly the TPS - especially since it's an "off idle" response...
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Old 03-06-2011, 11:32 AM   #6
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only thing that kinda gets me wondering is why the 15-20 mins before it starts up again just fine? what would cause it to do that?

I'm about to head over to my local parts store to pick up some 2 cans of carb/throttle body cleaner.
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Old 03-06-2011, 11:42 AM   #7
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only thing that kinda gets me wondering is why the 15-20 mins before it starts up again just fine? what would cause it to do that?

I'm about to head over to my local parts store to pick up some 2 cans of carb/throttle body cleaner.
I can be wrong but think it's a small flood just before the off-idle stall-out and it's wetting the plugs. Waiting 15 or so allows the plugs to dry off.

Is there a "sticky" feeling to the pedal when coming off-idle? Do you "feather" the throttle when you restart or keep you foot off the pedal entirely? Try "feathering" if you have not done so already.

Borrow the code scanner while at the store and read/record/clear any codes you find.

If you end-up needing an IAC or TPS then buy OEM parts. They may be more expensive but you get what you pay for (hard lessons learned).
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Old 03-06-2011, 11:54 AM   #8
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I can be wrong but think it's a small flood just before the off-idle stall-out and it's wetting the plugs. Waiting 15 or so allows the plugs to dry off.

Is there a "sticky" feeling to the pedal when coming off-idle? Do you "feather" the throttle when you restart or keep you foot off the pedal entirely? Try "feathering" if you have not done so already.

Borrow the code scanner while at the store and read/record/clear any codes you find.

If you end-up needing an IAC or TPS then buy OEM parts. They may be more expensive but you get what you pay for (hard lessons learned).

Thanks for your help!
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Old 03-06-2011, 12:12 PM   #9
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The next time this happens, VERIFY if you have spark.

Pull a plug, keep it attached to the plug wire, place the plug electrode near a good ground, have somebody else crank the engine while you watch.

Knowing if you have spark or not will help narrow this down a lot.

And if you don't have spark, but 15-20 minutes later you do, that means you have a component that is suffering from "thermal" or heat related failure.

The #1 cause of heat failure is the crank sensor. The #2 cause is the ignition coil.
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Old 03-06-2011, 02:28 PM   #10
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The next time this happens, VERIFY if you have spark.

Pull a plug, keep it attached to the plug wire, place the plug electrode near a good ground, have somebody else crank the engine while you watch.

Knowing if you have spark or not will help narrow this down a lot.

And if you don't have spark, but 15-20 minutes later you do, that means you have a component that is suffering from "thermal" or heat related failure.

The #1 cause of heat failure is the crank sensor. The #2 cause is the ignition coil.

Thanks!

It hasn't happened again yet, but I just took the throttle body off, iacv off, and tps off, cleaned everything and put everything back together. I don't notice anything out of the ordinary yet, but I only drove it for about 10 mins.



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Old 03-06-2011, 03:39 PM   #11
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How old is that IAC? I would replace that or the minimum give it a good cleaning.
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Old 03-06-2011, 04:50 PM   #12
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Man, that looked nasty in there. That was some gummy crud, huh? I hope you didn't push/pull on the IAC's pintle too much because that would break it (even though it might already be bad - don't worry, you'll know soon enough). Anyway, nice job cleaning up the TB, etc. It looks good now!
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Old 03-06-2011, 07:02 PM   #13
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How old is that IAC? I would replace that or the minimum give it a good cleaning.
No idea how old it might be, I just picked up the Jeep a month ago. I used some carb cleaner and a soft tooth brush to clean it...took some of the crud off, I wouldn't say all.


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Man, that looked nasty in there. That was some gummy crud, huh? I hope you didn't push/pull on the IAC's pintle too much because that would break it (even though it might already be bad - don't worry, you'll know soon enough). Anyway, nice job cleaning up the TB, etc. It looks good now!
Yea, the back bottom-side of throttle plate looked pretty nasty...carb cleaner makes quick work of it tho!! I think when it gets a bit warmer out, I might take the entire intake manifold off and give it a good cleaning.

I'll see if the problem persists...then at least I can start narrowing it down.


Thanks again everyone!!
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