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Unread 06-15-2012, 12:55 AM   #1
Rico25
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Rough idle and low RPM in drive...I need help

Hey everyone,
I have a problem I can not fix! I have an 04 sahara, it is idling rough in drive and the RPM's are between 300 and 500. I can not for the life of me figure out what's wrong with it. I have replaced the following:
- idle air control
- throttle position sensor
- new spark plugs
- had the spark plug gaps checked ( I'm not sure how to gap them)
- completely cleaned the throttle body and map
- used carbon cleaner ( seafoam engine cleaner)
- checked vacuum lines for cracks ( to the best that I can of course)
- oil change

I have brought it to 2 mechanic shops and a chrysler dealership, which cost me $100 just for diagnostic ( which they thought it could be the TPS)which it wasn't the issue. I have been checking around but I am at a loss. This all started when I changed the spark plugs about 2 months ago, they were in bad shape. I bought the car in august and it had 67k on it so I think they were original, now this rough idle showed up.

It idles rough when in drive and the engine is warm, it has stalled out on me a few times but started up again first time.

If anyone could throw me an idea on what I could check next, that would be great

Thnx

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Unread 06-15-2012, 01:09 AM   #2
Rico25
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I clicked the wrong thing while posting....any advice would help

Quote:
Originally Posted by Rico25 View Post
Hey everyone,
I have a problem I can not fix! I have an 04 sahara, it is idling rough in drive and the RPM's are between 300 and 500. I can not for the life of me figure out what's wrong with it. I have replaced the following:
- idle air control
- throttle position sensor
- new spark plugs
- had the spark plug gaps checked ( I'm not sure how to gap them)
- completely cleaned the throttle body and map
- used carbon cleaner ( seafoam engine cleaner)
- checked vacuum lines for cracks ( to the best that I can of course)
- oil change

I have brought it to 2 mechanic shops and a chrysler dealership, which cost me $100 just for diagnostic ( which they thought it could be the TPS)which it wasn't the issue. I have been checking around but I am at a loss. This all started when I changed the spark plugs about 2 months ago, they were in bad shape. I bought the car in august and it had 67k on it so I think they were original, now this rough idle showed up.

It idles rough when in drive and the engine is warm, it has stalled out on me a few times but started up again first time.

If anyone could throw me an idea on what I could check next, that would be great

Thnx

This is a re-post, any advise would be helpful
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Unread 06-15-2012, 01:22 AM   #3
WindsorRenegade
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Did you get the correct plugs? Did you get new wires as well? Could be a fuel pressure issue maybe. Did the problem start immediatly after the plug change?


Welcome to the forum, btw! These guys will figure it out for you man.
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Unread 06-15-2012, 01:42 AM   #4
Rico25
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Thanks for the welcome, the shop put the plugs in but I guess I will check again. It started within a few days, it's a coil ignition and i didn't change it. I was told by the mechanic that the injectors are clean and dont know how to to check the pressure and the fuel pump is in the tank and I don't want to swop a tank on " what if".
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Unread 06-15-2012, 05:55 AM   #5
jeepinhokie
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i have a similar problem. 04 TJ with 42RLE. Engine idles around 3-400 RPM when its hot outside. Not terribly rough, but you can tell that its stumbling over itself. put it in neutral and the RPMs climb up at touch and the rough idle goes away.

Ive cleaned my throttle body replaced my TPS. IAC is next on the list to replace.

interested in seeing what becomes of this.

i would suspect that your plugs are not the proper ones; and thinking about it, that might be my problem.
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Unread 06-15-2012, 06:19 AM   #6
BioTex
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Not sure if an 04 has plug wires or the later style wireless ignition, but here's what I would check. Since you didn't install the plugs yourself, you have no idea if one was dropped, or who knows what, but start with the simple stuff.

Check the firing order. Maybe two wires got swapped around. Check that the boots are seated. Sometime removing a wire to change plugs, the wires become damaged because the mechanic pulls on the wire and not the boot.

A quick and easy test is to take a spray bottle of water and set it to the stream spray position. With the engine running, spray a squirt directly on the exhaust manifold right were it exits the head. The water should instantly turn to steam. If it puddles any, that cylinder is misfiring, and you can norrow your search this way.

It doesn't get much easier than changing plugs and wires, and it is not very expensive either. Then there is the distributor cap and rotor next if the new wires don't fix it. For these parts, it is cheaper to just replace them all than to pay someone to diagnose it.

Why did you pay chrysler if they didn't fix it?

Anyways, water under the bridge... Thry the water spray trick, and see if all cylinders look evenly the same temp at the exhaust. A heat gun works well, but you most likely don't have one huh?
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Unread 06-15-2012, 06:26 AM   #7
Rico25
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I did the IAC already, it was a dead end for me. I am gonna pull the plugs myself...which I should have done in the first place just didn't have the time.

Thnx hokie
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Unread 06-15-2012, 06:32 AM   #8
jeepinhokie
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Quote:
Originally Posted by BioTex View Post
Not sure if an 04 has plug wires or the later style wireless ignition, but here's what I would check. Since you didn't install the plugs yourself, you have no idea if one was dropped, or who knows what, but start with the simple stuff.

Check the firing order. Maybe two wires got swapped around. Check that the boots are seated. Sometime removing a wire to change plugs, the wires become damaged because the mechanic pulls on the wire and not the boot.
04 TJs have the same wireless coil rail as the 06's. so no way to get two wires swapped around.
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Unread 06-15-2012, 06:39 AM   #9
BioTex
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Quote:
Originally Posted by jeepinhokie View Post
04 TJs have the same wireless coil rail as the 06's. so no way to get two wires swapped around.
Ok, I thought they did, but posted that anyways for others that need to localize a missing cylinder.

What year did they do away with the wires?
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Unread 06-15-2012, 06:43 AM   #10
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Quote:
Originally Posted by BioTex View Post
Ok, I thought they did, but posted that anyways for others that need to localize a missing cylinder.

What year did they do away with the wires?
not sure, but i would assume its one of the differences between 97-02 and 03-06. but thats just a guess
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Unread 06-15-2012, 07:28 AM   #11
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Maybe o2 sensors. Are you getting any codes on it? Mine was rough as well, ended up changing out the trans mount to a new rubber one. MUCH better now.

Also find out what plugs were put in. They are so simple to change on the Jeep with no coil or wires to worry about.

Another thought, push down on the coil pack as well make sure they popped it down onto the plugs and they tightened up the 2 bolts that hold it on
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Unread 06-15-2012, 08:08 AM   #12
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personally. mine has been doing it for a while now. its not bad in the winter when the weather is cold. but when the weather hits 70+. the engine will stumble a bit when stopped at a red light in gear when the engine is warmed up. (engine temps all in normal ranges)

at least for me, the main problem is the RPMs dropping so low, which causes a rough idle.

i cant imagine what the trans mount would have to do with RPMs. But Ill be replacing my trans mount this weekend for a custom crossmember, so ill be able to rule that out here shortly.

could a clogged trans cooler (inside radiator) cause the trans to build up pressure and cause the engine to stumble? curious about why mine only does it in gear.

OP, what trans do you have? manual/auto?
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Unread 06-15-2012, 01:05 PM   #13
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Quote:
Originally Posted by biotex View Post
what year did they do away with the wires?
On 2000 4.0L...
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Unread 06-15-2012, 06:00 PM   #14
Rico25
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Quote:
Originally Posted by Mboelts View Post
Maybe o2 sensors. Are you getting any codes on it? Mine was rough as well, ended up changing out the trans mount to a new rubber one. MUCH better now.

Also find out what plugs were put in. They are so simple to change on the Jeep with no coil or wires to worry about.

Another thought, push down on the coil pack as well make sure they popped it down onto the plugs and they tightened up the 2 bolts that hold it on
I was thinking about o2 sensors, any thoughts on which one I should switch out? How hard is it to do? I have never done one before
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Unread 06-15-2012, 06:04 PM   #15
Rico25
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Quote:
Originally Posted by BioTex View Post
Ok, I thought they did, but posted that anyways for others that need to localize a missing cylinder.

What year did they do away with the wires?
I am just asking around, if I were to tackle the o2 sensor next, any suggestions on which one I should change out? I know they have four but I have also heard that one or 2 don't really do much.... Is that true?
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