4.0L Rough Idle - Tried everything... any more ideas?

[Intense-Dakota]

2004 WJ w/ 4.0L and 4x4. I have replaced, plugs, IAC, TPS, Crank Position Sensor, removed and completely cleaned throttle body (with sensors out). I have done an oil change, checked motor mounts and trans mount (they seem to be ok).

It runs rough (not to the violently shaking, but rough enough to get a massage while sitting still) in Park, Neutral and all drive gears while sitting still (except for the first few second when I start up cold when the idle is still around 800-900 and then it drops to normal (around 550 rpm's). I just recently had it almost stall a few times when stopping at a light (RPM's did not seem to drop when it started to stumble). It will idle rough almost like rotational type of shimmy (hard to explain, but it will run rought for a second, then smooth for a second, then rough for a second and so on). It does not seem to be effected when the rpm's are any higher then idle. The tac always stays steady and does not fluctuate with the idle at all. Reseting the computer after changing IAC fixed the stalling for about 3 days. I reset the computer today when changing the CKP Sensor, and its not stalling, but the idle still seems to rough. The only things I have not checked or changed yet are the following:

Upstream O2 sensors
Downstream O2 sensors
Map sensor
Coolant temp sensor
IAT sensor
Fuel Filter/Regulator
Injectors
Coil Pack
Computer

I would rather not keep replacing parts with no change (except resetting the computer. I do have a warranty on it, but I have a $100 deductible so I am currently just replacing all the parts that would run less then $100. I have already had it in the shop 2 times, and they say (the famous I realy should'nt be a mechanic saying of) "We ran the diagnostics through the computer and it said everything was fine", so I really don't want to take it back again. I do have a vacum gauge, but not sure if that would help diagnose it or not (I use it to tune my dart, never on a fuel injected vehicle).

BTW- There is no check engine light, and I have pulled the codes 3 times with nothing showing (using the key trick 2 times, and AutoZone pulled once).

If anyone has any insight into this at all, even if one of the "havent changed parts" fixed your idle issue , please, please, please, please let me know.

 

[Bounty__Hunter]

(not to the violently shaking, but rough enough to get a message while sitting still)

What's this message you speak of?

 

[Intense-Dakota]

wow, thanks for being the worlds greatest human spell checker - you were biggest help I have had this year, don't know what I would do without your informative post.

 

[Bounty__Hunter]

I'm trying to get you to clarify your post, thought maybe your jeep had some message center that showed something besides an error code. Don't be so defensive, I didn't even know it was a typo until thinking about your second post and finally getting it. I'm slow.

I'd help if I could, but your smart-alec post is making it tough.

 

[Intense-Dakota]

i appologize, I was a little mad at my jeep, and took your resonse out of context. I am not recieving and messages or check engine lights at all.

 

[mud4feet]

How about your plug wires? Though, if you've got one bad enough to cause a miss, it should throw the CEL.

How'd your old plugs look?? Any indication of anything amiss??

 

[Intense-Dakota]

New problem!!! Today when I went to start the jeep on lunch, it clicked (like the battery was dead) one time, the Trip and overhead milage reset to 0, but the radio stations are still there, and then started. Then once running, the dash voltmeter was doing some super strange things as seen in the linked video. I tried giving it gas to bring the idle up, but the idle speed made absolutely no difference in the voltage readings. The WJ's dont have plug wires, but I did replace the plugs with no change. This time i went with the recomended NGK plugs. The old plugs looked good except for a bit of carbon build up of plugs 4 and 6.



www.mopar4life.com/pics/MOV00012.mpg

Please help if you can.
Thanks,

 

[Intense-Dakota]

Ok, more testing -

Battery w/ jeep off - 12.2-12.8v
Battery During Start - Lowest 5.4v Highest 11.6v
Running with accessories off 13.94v
Running with lights, AC at full and Radio 11.98-12.82v

However, even those these (except for starting) ar all pretty consistant, the volmeter on the dash is still moving quite a bit (not as much or as fast as in the video) but the volt meter hooked to the battery is not moving at all.

 

[mud4feet]

.......The WJ's dont have plug wires..........

:shock:???????? NO plug wires????? How do the plugs get juice?????

Gotta say, that's a new one on me.

 

[Intense-Dakota]

coil over plug design - (i.e. there is a coil rail that sits on top of the plugs).

 

[mud4feet]

coil over plug design - (i.e. there is a coil rail that sits on top of the plugs).

Did a google search.................learn somethin' new everyday!! Thanx for clearin' that up for me - sorry I can't help.

 

[Intense-Dakota]

Yesterday, picked up a new battery and installed it.
Today, the voltage is still acting crazy (see video link above if you havent)
So, I went to autozone and had them test the alernator while it was in the Jeep. Below are the readings at 2000 rpms.

peak voltage: 13.46
peak amps: 88.6
(They said that was good - that was with no lights on, just the radio on but turned down and the AC on low)

I have checked all battery cables and all the grounds I can find. I have also determined that the voltage seems to go up a bit once stopped, but after sitting for about 30-45 seconds, it starts to come down again and starts moving around again. It also seems that the Jeeps idle seems to be rougher when the idle drops a bits or starts moving around.

 

[dbxtr3]

I would stay you have a bad alternator. AZ has told be a alternator was good before when I know it was bad. A company car at my work is a 2000 Grand Cherokee Limited 4.7 that was doing the same thing when the alternator went bad. I am the company mechanic.

 

[97teejay]

Did you put a multimeter on the back of the alternator to verify that the readings your getting on the dash are the same as what is coming out of the back of the alternator. Easy way to determine you have a issue with your voltage regulator on your alternator or not before you go buy another alternator.

Have you put a fuel pressure gauge on the rail (if your 4.0 allows it) you should verify proper fuel pressure at key on, idle, and 2000 rpms.

Do you have a injector pulse width tool? you can back probe your injectors to verify that the injectors have a good "heart beat" and are firing like they should, if you had a bad injector it would flash irregular.

I'm a marine mechanic but almost 90% of what i work on is MPI so these are all steps i would take once you verify that it is in proper tune... if you have two plugs that look different than others i would be suspect to injectors.

 

[SteelHeadz]

Safety Recall D-13 issued out on March 04 involves the replacement of the crankshaft sensor. i saw you have mentioned you replaced that sensor. you might be able to get a refund on that from a dealer. They would need to verify the build date of your jeep to see if its involved in that recall.FYI.. as far as the idling concern, it might be better to just pay for the Deductible.i cant blame you for feeling the way you do towards the Dealer you took your jeep to. some of them can be arrogant and condescending. However, if you could help it, there is at least a couple of things they can verify in regards to a TSB that i've checked.Technical Service Bulletin. Ask them if they could check for relevant TSB's on the Performance section of the Chrysler Tech. connect.

 

[malton]

for the alternator, i'd go to advance auto if there's one near you; their tester has an old-school analog VU-meter or whatever it's called, easier to spot tiny random fluctuations that shouldn't be. in my case, when the engine fired up the alternator's initial voltage was way under spec but somehow it pretty quickly juiced itself up, quickly enough to fool everyone else's testers. replaced it and immediately quit throwing codes and killing batteries....

 

[DonnieB]

I had same problem that a can of "SeaFoam" Fuel Treatment helped. The rough idle comes and goes sometimes but, it did run smoother.

 

[audioatg]

Check the injectors. Take a stethoscope and listen to each injector. You wanna listen for a metal to metal clap slap whatever you wanna call it. If they have a dull thud. Thats your rough idle.