Sticky idle

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getdealtwith

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A few months ago, my mechanic replaced the IAC on my 04 Navigator (5.4 32V) with an aftermarket unit. It's the same type the Expys use.

Idle control has been fine until I recently cleaned MAF and intake air temp sensor as my MPG is still really crappy on this SUV. I used MAF cleaner as usual.

Afterwards, I noticed that I started getting a sticky, lagging high idle. If I roll to a stop sign and shift into N, RPMs jump to 1200 to 1500 and the IAC takes 3-4 seconds to regulate air intake down to 750RPM. If I stay in D, this high idle will push the truck forward so I have to brake harder.

When I unplug the IAC, idle drops much quicker and more like on my Expedition.

I removed the unit to inspect it and it's clean and seems to function OK. I also replaced the MAF with a quality part since the problem started after I cleaned it. There are no vacuum leaks or codes.

Has anyone had a new aftermarket IAC go bad on them? Or could this be a PCM issue? Before I swap parts with my Expy or buy a new one, thought I'd post this here to see if others have encountered this same issue and how they fixed it.
 
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getdealtwith

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Ordered, thx. Will report back.

Follow up note about poor MPG, how many here have actually had a fuel injector leak or stuck open engine off?

I get light gray smoke upon startup in a year round warm climate and definitely have a coolant leak. It smells like very rich combustion.
 
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getdealtwith

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No codes. I don't have a fuel pressure gauge. Would need to get that tested. Thanks!
 

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Need to do a relearn... disconnect battery and ground out positive for a few minutes. This will wipe out all learned settings. It is free and fixed my iac when I changed out mine. Idled high till I did the relearn.
 
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getdealtwith

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Need to do a relearn... disconnect battery and ground out positive for a few minutes. This will wipe out all learned settings. It is free and fixed my iac when I changed out mine. Idled high till I did the relearn.
On 03-04s? I thought relearning was only needed for 05 and up with full electronic throttle control?

Either way, I had the battery disconnected overnight, installed a Motorcraft IAC w new gasket and it idles correctly now. I didn't perform any learning procedures though.
 

the bus

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On 03-04s? I thought relearning was only needed for 05 and up with full electronic throttle control?

Either way, I had the battery disconnected overnight, installed a Motorcraft IAC w new gasket and it idles correctly now. I didn't perform any learning procedures though.
Yep you had the battery disconnect long enough to clear all the learned positions. The quick way is to ground out the positive cable. Glad it is running good again!!
 

riphip

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Also look for vacuum leaks. Will give false info to computer & will add fuel to compensate. Vacuum lines are rotted from engine heat, age, etc.
 
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