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Unread 10-30-2013, 04:33 PM   #1
Zelzuk53
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'06 Grand Cherokee V8 rough idle and erratic RPMs

I love my V8 to death, but it started having some idle issues and general loss of power around 4 months ago.

It all started the day after I replaced my AC blower motor and resistor. The next day I was sitting in terrible DC traffic, probably idling for about 3-4 minutes and when I went to press on the gas I realized that I had completely lost power. It wasn't idling rough or anything--it just went quiet. The radio never stopped playing, so it can't be a battery issue. This happened again the next day after idling for about 3-4 minutes. For the next two weeks it was sluggish and just felt like I was basically coasting everywhere.

I took it to my mechanic, but they couldn't recreate the problem. No codes, no nothing. Auto zone tested the battery and the alternator and everything checked out fine. I kept stressing that my RPMs were outrageously low for what I was used to. As soon as they dropped below 500 it threatened to stall out.

I ended up taking matters into my own hands and I replaced the spark plugs (some of the old ones had melted down), the air filter, gas cap, dumped a can of seafoam cleaner in the gas tank and I would have replaced the fuel filter but it isn't accessible. The dealership also reflashed my PCM. I could definitely tell a difference power-wise after doing all of these things but I was still idling at around 500--sometimes 600 RPMs on a GOOD day.

The jeep seemed to pep back up until a couple weeks ago. I was starting to idle rough, shifting seemed a little off, and it was driving kind of rough even on the highway. Now when I idle the RPMs wiggle up and down between 600 and 300. I started shifting it into neutral to raise the RPMs but they dance there too. Now when I'm in park they'll drop down to 300-400 and then rev up sometimes to 2,500 over and over again.

In attempts to fix it I replaced the Idle Air Control Valve (the old one was completely black) and the throttle position sensor. I've driven it about 150 miles since and it's shifting better overall but the problem still persists. I've been warned by multiple people about cleaning the throttle body out so I'm a little hesitant but at this point I'm getting kind of desperate.

What does everyone suggest I do next? I was planning on going ahead and replacing the PCV valve and at some point I'll probably replace the fuel pump assembly.

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Unread 10-30-2013, 04:36 PM   #2
Jeepforthewin
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I would go ahead and replace the PCV valve.
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Unread 10-30-2013, 05:15 PM   #3
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Do you bother to clean the throttle body or did you just change out the iac valve? There are passage ways for the iac to bleed air in that become clogged just like the iac itself.
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Unread 10-30-2013, 06:12 PM   #4
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Yes, I spent a good amount of time cleaning that passage way carefully with carb cleaner and a cloth. I went back as far as my fingers would fit.
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Unread 10-30-2013, 08:26 PM   #5
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You can just blast it out with the spray can... I use brake cleaner. I'll sometimes use an old toothbrush where it will fit.

What about the tps? If it's on the fritz it could be fooling the pcm into thinking the throttle is moving
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Unread 10-31-2013, 06:39 AM   #6
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Just replaced the tps. Should I unplug my battery and let everything reset?
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Unread 10-31-2013, 07:53 AM   #7
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I've never bothered resetting the PCM for anything.

The PCV isn't going to cost you much time or money to replace, but it won't be causing these problems. Hell, I've never bothered to replace one before.

The fuel pump isn't your problem either. Don't go shotgun mechanic on it replacing parts you don't need to.

I think you need to revisit the IAC valve and it's ports thoroughly. Be sure you have no vacuum leaks as well.
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Unread 10-31-2013, 10:01 AM   #8
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What's the best way to check for those leaks? The previous owner owned this car at the beach and the salt water has definitely caused some corrosion.
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Unread 10-31-2013, 11:31 AM   #9
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Do you hear any whistling (loud to moderate) that you can tell for sure isn't coming directly from the throttle body?

You could also spray a small shot of carb/brake cleaner at the hose connections or other suspect areas. If the idle goes up in relation, there would be a leak there.
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Unread 10-31-2013, 12:51 PM   #10
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I'm not sure if I've heard a whistling...a whirring sound maybe, but I've only heard it while I've been driving. I HAVE heard a weird almost clicking sound coming through my a/c vents. Another weird thing that happens is the air will never fully turn off. After I turn the a/c off it still blows out whatever the last temperature setting I had it on. Not a lot but definitely enough to notice it. I'm sure that has something to do with the blower motor that I installed a few months ago.
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Unread 10-31-2013, 01:16 PM   #11
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I get some strange RPM jumps too, mostly after letting off the gas (already changed the TPS). I did clean the IAC/TB, but I'm just going to replace it (IAC) this weekend. I may take jeepforthewin's advice and change the PCV. We'll see how it goes..
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Unread 10-31-2013, 02:09 PM   #12
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How'd your IAC look when you pulled it out? Mine was a booger to get out and completely black inside. My tps looked fine, but then again not sure why it wouldn't. I wouldn't know what to look for besides carbon buildup.
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Unread 10-31-2013, 07:12 PM   #13
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I took the jeep in to my shop for a general oil and fluids change and to see if they could see something that I was missing, but they couldn't find anything beyond the coolant leak that I already knew about. It feels like it's driving a little smoother on the highway, but tonight when I turned my lights on I noticed that the lights on the dashboard and console were both extremely dim. Is that the ignition switch? It was replaced less than a year ago.
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Unread 10-31-2013, 07:26 PM   #14
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Could possibly be your alternator.
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Unread 10-31-2013, 07:47 PM   #15
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That's bad news. However, I'm almost glad another symptom has popped up because it pushes me in the right direction. I had them test both the battery and alternator at autozone. Both seened alright. My brother hooked my battery up to his own personal charger and it took about an hour to fully charge. What should the battery and alternator be reading when hooked up? Maybe it's possible that I've pulled on something too much or wiggled something to hard while I was working. I don't want to blindly replace the battery or alternator without knowing exactly which one it could be.
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