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Old 08-06-2013, 01:49 AM   #1
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Rough idle + slight misfire

Hello,i have an 06 jeep rubicon 4.0 mt .now that I have more or less figured out my mpg problem I have another issue( not as pressing but still). Went out and fired up my jeep to go to work and every thing was fine when the motor is cold and idle is higher but once the motor reaches operating temp and down it starts idling a bit rough. Now it's not kicking on the mil light nor is it wanting to die but it feel like there is a slight misfire or not getting enough fuel or something. I read in another forum that it could be an issues with heat and where the injectors set into the manifold. Anyone else have this problem.

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Old 08-06-2013, 02:02 AM   #2
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I had something to it on both my jeeps one was an O2 sensor and a tps sensor.. People say O2 sensors are never it just try unpluging it and find out which cylinder is miss firing and then switch the injector if the miss fire moves boom found the problem or also check the coil pack check it at night if u see a blue spark arch its a coil pack

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Old 08-06-2013, 09:43 AM   #3
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Starting with the basics, how old are your spark plugs? If they aren't that old, exactly what brand & model spark plug did you install?
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Old 08-06-2013, 11:03 AM   #4
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That definitely sounds like your TPS. If it kicks the check engine light take it to an auto parts store for a free test
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Old 08-06-2013, 11:09 AM   #5
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Starting with the basics, how old are your spark plugs? If they aren't that old, exactly what brand & model spark plug did you install?
Plugs are champs 7704 put in a couple of days ago. Also put all four new o2 sensors in with NTK brand. I pulled and cleaned the IAC and ran a bottle of 44k in it. Only real weird thing in all that was when I replaced the coil boots and inner springs, the very front boot spring was hard to pull out so I ended up stretching it and it finally came out. I put the new stuff on and they seemed to fit nice so IDK if I my have damaged it.
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Old 08-06-2013, 11:10 AM   #6
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That definitely sounds like your TPS. If it kicks the check engine light take it to an auto parts store for a free test
No mil light. I have a scanner and nothing came up
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Old 08-06-2013, 05:14 PM   #7
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Update: I went ahead and replaced the IAC and TPS and still did not fix the problem I'm now starting to wonder if my injectors are getting heat soaked
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Old 08-06-2013, 05:17 PM   #8
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Hmmmm did you look in to your distributer at all
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Old 08-06-2013, 05:44 PM   #9
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It's a DIS system
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Old 08-07-2013, 11:00 AM   #10
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Originally Posted by Jerry Bransford View Post
Starting with the basics, how old are your spark plugs? If they aren't that old, exactly what brand & model spark plug did you install?
I'd go with Jerry on this one (because he helped me through a similar issue). I noticed with mine that I had one plug that was gapped just a hair off and caused my misfire. If it isn't your plugs, it could be a heat soak issue. I had to replace the heat shield under the injectors on mine, old and falling apart. I also placed a sleeve around the number 3 injector. I think there is a thread on here with part numbers. The DIS is very finicky I've come to notice.
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Old 08-07-2013, 02:02 PM   #11
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I'd go with Jerry on this one (because he helped me through a similar issue). I noticed with mine that I had one plug that was gapped just a hair off and caused my misfire. If it isn't your plugs, it could be a heat soak issue. I had to replace the heat shield under the injectors on mine, old and falling apart. I also placed a sleeve around the number 3 injector. I think there is a thread on here with part numbers. The DIS is very finicky I've come to notice.
Does that sleeve cover the 06 4.0, I thought it was for the 02-04 models
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Old 08-07-2013, 09:34 PM   #12
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Not going to say it isn't, but the more common problem with the injector shields was a hot soak problem. After the vehicle was driven, parked for a bit, and then restarted.
Would cause a fuel starvation problem, like vapor lock. Making hard to start, running poorly until enough cool fuel got through the injectors. Can't say I remember it causing a problem in normal driving.

I'm with Jerry, always start with the basics.
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Old 08-07-2013, 11:16 PM   #13
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Not going to say it isn't, but the more common problem with the injector shields was a hot soak problem. After the vehicle was driven, parked for a bit, and then restarted.
Would cause a fuel starvation problem, like vapor lock. Making hard to start, running poorly until enough cool fuel got through the injectors. Can't say I remember it causing a problem in normal driving.

I'm with Jerry, always start with the basics.
I'm using champs
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Old 08-08-2013, 12:30 AM   #14
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Not going to say it isn't, but the more common problem with the injector shields was a hot soak problem. After the vehicle was driven, parked for a bit, and then restarted.
Would cause a fuel starvation problem, like vapor lock. Making hard to start, running poorly until enough cool fuel got through the injectors. Can't say I remember it causing a problem in normal driving.

I'm with Jerry, always start with the basics.
I'm using champs 7704 I think. There double plats the dealer sold me
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Old 08-08-2013, 12:38 AM   #15
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Update: took her to a friends shop and scanned it. Well it looked like the voltage didn't change during the misfire to the injectors ( that does not rule out an injector going bad) but it seems like there really dirty according to him, so I'm going to run an injection system flush and see if that helps
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Old 08-08-2013, 10:46 AM   #16
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I seriously doubt your injectors are dirty, I would bet big $$$ flushing/cleaning the injectors won't help at all.

Champion 7704 plugs are the wrong model, 7034 is the right double-platinum model Champion spark plug for newer distributorless engines like yours.
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Old 08-08-2013, 07:43 PM   #17
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I seriously doubt your injectors are dirty, I would bet big $$$ flushing/cleaning the injectors won't help at all.

Champion 7704 plugs are the wrong model, 7034 is the right double-platinum model Champion spark plug for newer distributorless engines like yours.
I could not remember the number 7034 are what I put in
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Old 08-28-2013, 10:48 PM   #18
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Update: well the idle is still rough. I gapped the plugs again and ran some 44k thou it, and that helped for a little. Still can't seem to pin point the problem. It never stalled out it just seems to me like a misfire. I'm hoping to find the cause soon
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Old 08-29-2013, 03:26 AM   #19
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I seriously doubt your injectors are dirty, I would bet big $$$ flushing/cleaning the injectors won't help at all.
X2 This guy is a smart cookie

I have yet to see with my own eyes injector cleaner work if its to the point there not spraying right it is time to replace them.
As for your slight miss it could be injector going bad or coil starting to fail. I would lean more toward coil.
Try a different set of plugs. I had an outboard do the same thing and figured out it did not like platinum plugs it ran better with old school no frill spark plugs
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Old 09-07-2013, 01:11 PM   #20
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Update: I ended up putting on a new coil ( I dropped it ) and still idling rough.
I'm still thinking it has to do with the fuel injectors.
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Old 09-07-2013, 01:22 PM   #21
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Update: I ended up putting on a new coil ( I dropped it ) and still idling rough.
I'm still thinking it has to do with the fuel injectors.
How is it doing when driving any missing or backfires or doing anything while driving?
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Old 09-07-2013, 04:21 PM   #22
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How is it doing when driving any missing or backfires or doing anything while driving?
well.. it drives great, no rough idle,no mis,nothing
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Old 09-10-2013, 11:53 AM   #23
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Well we had a big temp drop were I live ( roughly 20 degrees colder ) and my jeep was running pretty good. The misfire and rough idle was still there but hardly noticeable. So I wonder what it could be?
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Old 09-10-2013, 05:48 PM   #24
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Well we had a big temp drop were I live ( roughly 20 degrees colder ) and my jeep was running pretty good. The misfire and rough idle was still there but hardly noticeable. So I wonder what it could be?
I wish I could help you but I don't know I wonder if there is a air/temp sensor that could do that? I doubt it what about o2 sensor I will think more about it but I am unsure
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Old 09-11-2013, 11:47 AM   #25
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I wish I could help you but I don't know I wonder if there is a air/temp sensor that could do that? I doubt it what about o2 sensor I will think more about it but I am unsure
All foyer o2 sensors are new
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Old 09-11-2013, 12:57 PM   #26
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I'm actually running into a very similar issue on my 03 Sport, though my miss occurs at all times from startup to fully warm. No CEL. I'm debating buying a rebuilt injector set. Have new plugs, new coil, cleaned throttle body, air filter, checked TPS.

If you haven't done that last thing, give it a shot. Easy to do - you can backprobe the connections with a multimeter. The center one is ground, one will have constant 5v(ish) power, and one will move from very low up to around 5v depending on throttle position.
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Old 09-11-2013, 11:15 PM   #27
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My 03 runs a bit rough at idle as well. I've cleaned the injectors twice in the last year and both times it runs much smoother afterwards but it only lasts for a month or so. I've also noticed on a couple trips that if I buy fuel with no ethanol that it will also idle smooth. Eventually I'm going to replace the injectors, since cleaning them does seem to alleviate the issue for awhile.
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Old 09-11-2013, 11:31 PM   #28
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I'd bet more on one or both of your upstream 02 sensors being bad, I really doubt your fuel injectors have anything to do with your rough idle.
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Old 09-12-2013, 06:49 AM   #29
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I'd bet more on one or both of your upstream 02 sensors being bad, I really doubt your fuel injectors have anything to do with your rough idle.
I'm having a rough idle issue that vibrates the cab to the point that the mirrors shake. The engine feels like it stutters every few seconds but never dies. When I hit the gas everything smooths out and runs great. I've cleaned the IAC, swapped plugs, and plan on testing the TPS. Do you think the O2 sensors would be worth changing? I don't understand why the engine is rough while at idle but runs great while driving. I just got the jeep (04 unlimited), not sure if it should be idling like this or not.
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Old 09-12-2013, 12:02 PM   #30
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Here's the thing about the O2 sensors, and why I ruled them out in my own situation:

Firstly, there is no CEL. This doesn't necessarily mean they are not at least somewhat faulty, but is a good start.

But when a vehicle is first started, it runs in open loop - completely bypassing the O2 sensors until it warms up and then goes into closed loop. So if the idle/running occurs when the vehicle is dead cold, then it shouldn't be the O2 sensors.

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