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P0507 :-(

31K views 124 replies 9 participants last post by  stevestloo 
#1 ·
Hey guys,

Couldn't find anything on here with the search function.

I have a 2006 LJ w/ the 6speed manual and 96K miles
Check engine light came on with code P0507

"P0507 - Idle Air Control System RPM Higher Than Expected"

and the "possible causes" list is a mile long.
I was hoping if I listed some symptoms that it would narrow the problem down:


The vehicle idles at 1000 to 1050 or so RPM whether cold start or warmed up. Because of this higher idle I can't really listen that well for vacuum leaks.

When I am cruising down the road, the RPM's tend to want to stay in place until I just about come to a stop, which is when it returns to the 1000 or so idle.

Even at a complete stop, if I give it gas in neutral, the RPMs will go to wherever they go, say 2000RPM, and has a hard time coming down to idle level.

I did feel around some of the vacuum lines and I did not feel anything, but like I said its pretty loud. The crankcase vent elbows and grommets are new also.

I don't mind throwing a part or two at the problem, but if any of the above sounds like something obvious please let me know! Thanks!!

:cheers:
 
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#6 ·
Before I do this, I seem to have the 4861552AC part in my 06 which looks.. funny to clean.. I was thinking just remove it and get in there with a toothbrush and throttle body cleaner and go to town, but it looks like theres a bunch of nooks and crannies that would seemingly get gunked up.. should I just proceed?

 
#7 ·
Clean IAC
Check for vacuum leaks.
Check for manifold leaks, or any leaks after throttle body.
Use carb cleaner and spray around manifold and areas where you check. If idle changes, that's where you got a leak. Sounds like possibly unmetered air issue.

Post back!
 
#11 ·
Here are the "after" pics:

Throttle body "top" (air filter side)


Throttle body "bottom" (engine intake side)


IAC clean!:

--------

So after all of that, this didn't fix the problem. Still idles around 1100RPM.. the only way I can get the RPMs to go below 1000 is to pop it into 6th gear when I'm going super slow, and even after that, while idling, the vehicle attempts to get back to that 1100-1200RPM idle. I can still "crawl" without pressing the gas pedal, and the RPMs still don't drop.

SO after all of that, the problem persists!

I used some of the the throttle body cleaner to spray around the vacuum hoses near the air intake to see if the idle would change, and I couldnt.. so I dont think I have a leak.

After cleaning the IAC I made sure the piston (is that what it is?) moved up and down freely and it did, felt springy and returned to the closed position.

I must have a bad IAC (or whatever controls it, which I think is the computer??)

Thanks for looking :)
 
#16 ·
One way you can test, is too pull it, put it in a vice, and heat the end inside your exhaust with a torch. Have a multimeter hooked up and reading. The voltages should change. Its gonna be between .2 and .8. If it doesn't move due to heat, it's bad, if it were to go over 1v, it's bad. If it's 4-pin then it's got a pre-heater circuit, and that can be tested for continuity, as sensor needs to be up to temp to do its thing hence the second set of wires.

I'm gonna check when I get off work to make sure on numbers and actual procedures for you.
 
#18 ·
Yeah just trying to play the logic game and narrow it down. Something is allowing variable amounts of air into the intake. Today after work I'm going to make sure the throttle is actually fully closed when idling, which I'm 99% sure it is otherwise I think I would be getting TPS related codes.

Really, though, if the IAC was stuck open, is that even enough air getting passed it to keep my RPMs as high as 2200 to 2500 while I roll to a stop?
 
#19 ·
Strange to say the least. I wouldn't imagine the IAC has "control" at that rpm range. But Ive never done much other than clean them chasing down hesitation and loping idle issues.

I did some reading and some Mopar vehicle owners have had problems after cleaning a throttle body with throttle body cleaner. Apparently there's a sensitive coating on inside of throttle body. Complaints of butterfly not closing. Maybe your "throttle not closing fully" idea isn't off...as far as TPS codes, wouldn't it only throw a code if the actual sensor was bad?

Keep posting
 
#21 ·
I read the factory service manual on it this morning-PCM controls the IAC with 4 wires-two 12v and two ground. The different power circuits allow the IAC motor to be turned in both directions. IAC is tied into AC Compressor,power steering and vehicle speed sensor(mounted on transfer case). The IAC is controlling the amount of air that bypasses the throttle plate. At idle the IAC motor retracts a motor Pirtle allowing more air to pass through the port
I didn't see any testing procedures but the above may help you understand what all is in play. I would chase vacuum leaks, inspect connectors at the components noted and the wiring back to the IAC. If all is good I would then throw and IAC at it. If that didn't fix it I would get it in a shop so they can put a scanner on it. Could be one of the other components or the PCM at that point
 
#24 ·
Have you tested your TPS? I doubt it is bad, but never hurts to check. Another quick check is to disconnect the TPS and start the Jeep. If it idles fine, then the TPS is the problem. Here is the testing procedures for the TPS out of my 98 FSM

The TPS can be tested with a digital voltmeter.
The center terminal of the TPS is the output terminal.
With the ignition key in the ON position, check the
TPS output voltage at the center terminal wire of the
connector. Check this at idle (throttle plate closed)
and at Wide Open Throttle (WOT). At idle, TPS output
voltage should be greater than .350 millivolts but
less than 900 millivolts. At wide open throttle, TPS
output voltage must be less than 4.5 volts. The output
voltage should increase gradually as the throttle
plate is slowly opened from idle to WOT.
 
#27 ·
Well heres an update:

Have you tested your TPS? I doubt it is bad, but never hurts to check. Another quick check is to disconnect the TPS and start the Jeep. If it idles fine, then the TPS is the problem.
I disconnected the TPS, and started it up. It hesitated at first, but after it started, it still idled high. This also made the check engine light come on (naturally.)


Here is the testing procedures for the TPS out of my 98 FSM

The TPS can be tested with a digital voltmeter.
The center terminal of the TPS is the output terminal.
With the ignition key in the ON position, check the
TPS output voltage at the center terminal wire of the
connector. Check this at idle (throttle plate closed)
and at Wide Open Throttle (WOT). At idle, TPS output
voltage should be greater than .350 millivolts but
less than 900 millivolts. At wide open throttle, TPS
output voltage must be less than 4.5 volts. The output
voltage should increase gradually as the throttle
plate is slowly opened from idle to WOT.

It could just be my technique but I got about 10-11 millivolts with the throttle closed, and no response from the meter by manually opening and closing the throttle. This was between the center wire (blue) and ground. I am going to try again in a little bit.. but I am fairly confident that I did this correctly.. though I feel that this would throw a TPS code!
 
#30 ·
You state that you sprayed carb cleaner around all of your hoses, etc. on the engine with no change in engine RPM. Are all of your HVAC controls functioning correctly? It surely sounds like a vacuum leak to me, but if one of your control hoses has come off under the dash the leak could be bad enough to cause this but not big enough to be noticeable over the cabin noise. Best way to check is to pull the vacuum lines off of the engine one at a time, put a cab over the nipple, start the engine and watch the RPM gauge.
 
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