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WJ 2004 Grand Cherokee limited 4.7 V8 idling question

8K views 25 replies 4 participants last post by  cheapjeep 
#1 ·
I fixed a cracked hose the other day going into my intake. It was idling low and stalling. Fixed the problem now it idles at 1100 sitting at a light and 1200-1300 in park. It now has so much power that once in drive or reverse it goes on its own before I accelerate. Is this normal?
 
#2 ·
No, it is not. It should idle at 650 rpm. Which hose was cracked?
If the hose enters the inlet after the throttle plate, then it normally causes high idle, since it bypasses the IAC. I would first have another look if no other hoses are cracked or loose. Also check the PCV valve. If its stuck open, then you also have a large airflow bypassing the IAC in idle.
Idle is regulated by the IAC stepper motor, so that would be the next thing i would look at. It normally gets quite dirty in there, so i would clean it out. If the IAC is working well and is clean (and the IAC air canal as well), then i would focus on the TPS. If you have a scanner with live data, then you can monitor the TPS%, which should be around 11-12% in idle.
 
#4 ·
Have a look as well to the hose which goes from the PCV valve to the engine inlet behind the engine. You can disconnect the hose at the PCV valve and keep it shut with a finger and see if the idle changes.
Do you have a scanner to check the TPS position?
 
#6 ·
If you have an android phone, then you only have to buy a cheap bluetooth dongle and download the free "Torque" app. This is always nice to have, also for future use.
Indeed strange that you had a low idle with a vacuum leak (which should be high normally) and now that the leak is solved, you have a high idle. The hose you repaired is it connected to one of the three connections on the throttle body, as shown on figure 27 in attachment?
 

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#7 ·
Looks like somewhere number 3 is. I had low idling issues for months with stalling at lights sometimes. Then I left work and the whole jeep felt like i was off roading when accelerating with a faint whistling noise from under hood. I'd I let off the accelerator it stopped. Fixed cracked hose and then vibration and noise quit but now idling high.
 
#8 ·
The vacuum connections don´t have a number on the drawing. #3 is the IAC stepper motor. But either of the three hoses broken or disconnected should give a high idle and not a low idle, since false air will be drawn behind the throttle blade and will bypass the IAC.
Did you try to disconnect the PCV hose and checked if the idle will change if you close the hose with your finger? There should be suction from that hose.
Did you check for fault codes using the key dance? ignition switch off/run three times and leave in run at the third time. odometer will show "DONE" when all ok, or a fault code(s).
 

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#9 ·
I haven't tried to disconnect the pcv hose. I have no codes. Check engine light hasn't even came on except every once in a while ill get the evap code which I think is just my generic gas cap. If I tighten that it goes off. I think tomorrow I'm going to fool around and check on the pcv hose.
 
#10 ·
First thing I would try is disconnecting the battery for 10 min or so.It may just have to do a relearn since you fixed the hose especially since its been leaking for a while.The pcm is sometimes slow to adjust to change in these things.
 
#12 ·
Disconnecting the battery for 1 minute already errases the PCM memory which holds the IAC stepper motor positions. After reconnecting the battery, the PCM will send the IAC to full open and full close and then sets it to a preprogrammed position. Then at the next starts it will relearn the right position.
That it idles that high seems to be or a vacuum leak, or the TPS which is commanding it to speed up. Did you check that the throttle cable is not binding and that the throttle is at its stop when not pressing on the accelerator?
 
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#16 ·
Disconnecting the battery for 1 minute already errases the PCM memory which holds the IAC stepper motor positions. After reconnecting the battery, the PCM will send the IAC to full open and full close and then sets it to a preprogrammed position. Then at the next starts it will relearn the right position.
That it idles that high seems to be or a vacuum leak, or the TPS which is commanding it to speed up. Did you check that the throttle cable is not binding and that the throttle is at its stop when not pressing on the accelerator?
Sorry buddy it don't always work by the book with the pcm on a wj.especially on a jtec board. For instance every time I had the batt disconnected on mine it refused to learn idle no matter what until i drove it down the road.After a lot of mods I've done I've had high idle issues until i did a relearn. I've modded that thing for 7 years and sometimes that book really doesn't mean squat when it comes to the real world.Try a relearn first is what I've learned with a wj and then move on to the other stuff.
 
#14 ·
Is that the one coming from the PCV valve? That is quite a thick hose, so gives a large vacuum leak and high idle. Still strange though that you had a low idle before.
 
#17 ·
I ment to say that it doesn´t take 10 minutes for the memory to errase. That on jeeps many things don´t go according the books, oh well:rolleyes:
 
#19 ·
I´m also not sure what Dave meant to say. Normally the PCM will do this by itself as far as i know, as soon as the memory is lost.
Did you already change the PCV hose?
 
#20 ·
I fixed the hose but did not reset the battery. Since everytime I mess with the battery it gives me issues. It still idles at about 1000 now but its not wanting to rev up and go on it's own now so that's a plus. Tackling the radiator tomorrow. Hopefully that goes well.



tomorrow so
 
#21 ·
I would still try an other battery reset and see what the idle will do and then drive around a bit, as Dave suggested.
 
#22 ·
Everyone always recommends going through the hassle of disconnecting the battery then reconnecting and have to put your radio settings and lose your trip and computer data. Do it the easy way and just yank the pcm batt 10 amp fuse in the fuse box next to your battery. So easy to do and you don't lose any settings.
 
#26 ·
I know if I disconnected the battery on mine for any length of time it would totally forget how to idle at all.Soon as you let off the gas it would just die.Only cure would be to take it for a couple mile drive and everything would return to normal.Wonder if that's the battery disconnect issue he's talking about? If so it's no big deal.
 
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