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  #1  
Old November 28th, 2012, 15:52
efrie004 efrie004 is offline
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4.0L Rough Idle with codes

I got my first check engine light, though the rough idle has been an issue since I got the Jeep.

The codes were as follows:

P0122 Which is a throttle position error

P0302 Says it's misfire on cylinder #2

I put a new TPS on the Jeep Saturday, and cleaned the IAC.

The previous owner put new wires, plugs, cap, and rotor on the Jeep last week, along with a new injector on cylinder #2.

As soon as I got it I put seafoam through the gas and changed oil + filters.

I cleared the codes this evening and it started running fine, but I cleared the codes Sunday and it ran fine again until this morning. I'm not quite sure where to go from here, I'm new to the realm of the 4.0L.

Jeep is a 98 for reference.
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Old November 28th, 2012, 16:12
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Ecomike Ecomike is offline
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Re: 4.0L Rough Idle with codes

Need to check compression, and inspect the spark plug appearance on #2 if the missfire code returns. Post a picture!!!
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34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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Old November 28th, 2012, 16:15
efrie004 efrie004 is offline
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Re: 4.0L Rough Idle with codes

What's normal compression for one of these with 179,000 miles?
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Old November 28th, 2012, 16:52
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Re: 4.0L Rough Idle with codes

120 is rock bottom. 150 is good, and IIRC 170 is max. No more that 30 psi difference between any two adjacent cylinders (In the firing order IIRC).
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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Old November 28th, 2012, 16:56
efrie004 efrie004 is offline
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Re: 4.0L Rough Idle with codes

Alright.

I know some of these codes can be caused by other issues, the XJ doesn't have a catalytic converter on it, but it looks like the post-cat 02 sensor housing was bumped out a bit using a spacer, which would be so it reads okay. I'm wondering if at this mileage, maybe the 02 sensors need to be replaced?

It's funny, I owned a MkIV Jetta 1.8T for nearly 5 years, I consider myself a sensor replacing king, but I'm still getting used to the Jeep's system. I don't know what causes what yet, etc.
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Old November 28th, 2012, 17:25
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Re: 4.0L Rough Idle with codes

things that can cause a bad idle?
  1. TPS (Throttle Position Sensor)
  2. Idle Air Control (IAC) motor
  3. Vacuum leak
  4. MAP sensor?
  5. Bad battery (effects ECU)
  6. Clean Throttle Body? (getting stuck?)
  7. CPS (Crank)
  8. Cam PS / Distributor Pickup Switch
  9. Distributor cap, rotor, wires, plugs
  10. Low fuel pressure?
  11. Bad alternator ?
  12. O2 sensors (should throw code)
  13. Bad injector?
  14. Replace coil?
  15. Intake Manifold Vacuum leak?
  16. EGR valve?
  17. CCV hoses clogged?
  18. Fuel filter?
  19. Air Temperature Sensor?
  20. Coolant Temp. Sensor
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Old November 28th, 2012, 17:37
efrie004 efrie004 is offline
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Re: 4.0L Rough Idle with codes

That's a nice list there, the top three have been gone over, haven't checked the battery yet.

Throttle body has also been cleaned. I guess I'll drive it for a couple more days and see if it comes back, I'll check the compression tomorrow.
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Old November 28th, 2012, 18:29
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Re: 4.0L Rough Idle with codes

As soon as the rough idle returns, check the code and post the actual code here!
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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