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Unread 04-11-2014, 09:23 PM   #1
Kapoosta
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2006 WK 
 
Join Date: Mar 2014
Location: Edmonton, Alberta
Posts: 31
General Thread of Idle Problems and Fixes

I see this issue a lot on the forum and the same things get mentioned each time so I thought there should be a general thread with all the possible issues and fixes. I am referencing a 4.7L V8 model with 545RFE transmission so things may be different for the 3.7L and 5.7L or with the NAG1

I have had to deal with the following problems:
Bouncing Idle / Flaring RPMs
Rough Idle / Low Idle

Which has also resulted in increased fuel consumption (from 14 L/100 km to 18 L/100km).

Through my research on the internet, I have come up with the following list. Please feel free to add something or argue anything that I have written. I do not know everything, this is just what I've taken from around the interwebs and what I've dealt with myself.


1. Low Transmission Oil Level

Symptoms: Low Idle while in Drive i.e. while stopped at red light (neutral and park seem to be fine for idle).
Causes: Oil leak somewhere. The transmission does not consume oil and so if you are low, it means you have a leak. Make sure to use this procedure to check you transmission oil level: OIL LEVEL CHECK. Note that you need to drive around for 15 miles for the transmission to actually be considered HOT. Going around the block will not do this but if you get it warm and the dipstick still shows around the "COLD" markings or below, you will know it is low.

Typical places for the leak are:
  • Around the transmission pan due to gasket failure/damage. Easy fix, just drop the pan and re-do the gasket. It is recommended to use RTV gasket rather than a pre-formed gasket.
  • Transmission oil cooler lines. Especially at the crimp connectors on the rubber portions. Lots of threads on this.
  • Sensors attached directly to the transmission have o-rings that may leak. There is a TSB about this.
Less Common:
  • Rear transmission oil seal at the transfer case. I had to do this one and it cost me $550 for labor and material. They also replaced the T-Case seals.
  • Front transmission oil seal at the torque converter (engine side of transmission) or torque converter is cracked/damaged. This one is much more expensive to replace due to having to drop the transmission. Dealer quoted me $1300 for this seal plus another $800 if the torque converter had to be replaced.
There is a vent on the transmission as well that should be checked and cleaned. I am going to do this as soon as I find it.. haha.


2. Idle Air Control (IAC) Valve Problem

Symptoms: Low Idle and/or bouncing idle.
Cause(s): Failure of component or it is dirty and causing it to stick.
Fix: Buy a new part (~$60 online) or remove and clean the one you have. It is easy to remove, just take out the one or two torx screws holding it on and disconnect the electrical connector. It is located on the side of the throttle body beside the TPS.


3. Throttle Position Sensor (TPS) Problem

Symptoms: Low idle, Bouncing idle, flaring of engine RPM's while driving, harsh up and/or down shifting (this scared me).
Cause(s): Failure of component.
Fix: Buy a new part (~$35 online). It is easy to remove, just take out the one or two torx screws holding it on and disconnect the electrical connector. It is located on the side of the throttle body beside the IAC valve.


4. Exhaust Gas Recirculation Valve (EGR) Problem

Symptoms: Low idle, weird shifting (i.e. accelerating in a high gear instead of downshifting), large decrease in MPG
Cause(s): Failure of component
Fix: Buy a new part (~$40 online). The location depends on your year, model, etc. Mine was at the firewall on the drivers side. You can find my writeup here:
http://www.jeepforum.com/forum/f67/a...-tube-2315345/


5. Restricted Air Flow to Intake Manifold

Symptoms: Low idle, poor performance
Cause(s): Clogged air filter, dirty throttle body
Fix: Remove your throttle body (make sure to disconnect negative on battery first) and clean it. There is a link in the Tech Write Ups thread. Replace the air filter.


6. Positive Crankcase Ventilation (PCV) Valve Problem

Symptoms: Low idle (not sure about this one..)
Cause(s): PCV valve has a spring loaded pin that allows crankcase vapors to escape based on the vacuum level. If the spring fails or it doesn't seal correctly, it won't work.
Fix: Replace the valve. The location is different depending on your engine, year, etc. Mine was beside the EGR valve at the firewall. This item is on the jeep maintenance schedule so it should be checked every 30,000 miles.


7. Spark Plug and/or Ignition Coil Problem

Symptoms: Low or erratic idle, loss of power, misfire
Cause(s): Old/dirty/broken spark plugs, incorrect spark plug gap, or a coil failure. Usually a complete coil failure will result in misfires.. but when one is on its way to failing, it is harder to notice.
Fix: Replace your plugs. Check your coils or buy a new coil and move the new coil around until you find the cylinder that had the bad coil.


8. Manifold Absolute Pressure (MAP) Sensor Problem

Symptoms: Low or erratic idle
Cause(s): Sensor is failing.
Fix: Replace the sensor. It is located on the front of the engine underneath the air intake box. Simple to replace with a torx bit.


9. Vacuum Leak

Symptoms: Low or erratic idle
Cause(s): Vacuum leak in one of the many vacuum lines around the engine.
Fix: Find the leak and repair it. People have had some success spraying carb cleaner around the vacuum lines while the engine is running which will cause the engine RPM to increase momentarily since the carb cleaner is combustible. The other way is to get a smoke test done but that requires expensive equipment or for you to take it into a shop.


10. Crankshaft or Camshaft Position Sensor Problem

Symptoms: rough idle, misfire, loss of power, backfire, bouncing idle
Cause(s): Failing component.
Fix: Replace the sensor.


11. Intake Air Temperature Sensor Problem

Symptoms: Loss of power, increased fuel consumption, low idle
Cause(s): Failing Component.
Fix: Replace the sensor.


12. Coolant Temperature Sensor Problem

Symptoms: This is how the PCM determines when to run in closed loop vs open loop. If the sensor fails, it will remain in open loop even at correct running temperatures. This may cause poor performance, high idle, increased fuel consumption.
Cause(s): Failing Component.
Fix: Replace the sensor.

and to think, after doing most of this stuff I still have a low idle haha.


Last edited by Kapoosta; 04-11-2014 at 09:34 PM..
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Unread 04-11-2014, 11:16 PM   #2
GoLeafsGo
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2005 WK 
 
Join Date: Feb 2014
Location: Ottawa, Ontario
Posts: 36
Great post.

Thanks for doing that, it really helps. Definitely gonna have to clean my throttle body in a couple weeks.
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Unread 04-12-2014, 06:53 AM   #3
thunderfgc
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2005 WK 
 
Join Date: Jan 2014
Posts: 93
Very nice. I'm experiencing the same symptoms with mine. Gonna start at the cheapest fix and work my way up haha. Thanks for all the info
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Unread 04-30-2014, 11:08 AM   #4
Jvenrick
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Location: Denver, CO
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Does anyone know the part # for a TPS for a 2007 grand cherokee with the 4.7L V8. Im having a real hard time tracking down the right part.
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Unread 05-02-2014, 10:17 AM   #5
Kapoosta
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2006 WK 
 
Join Date: Mar 2014
Location: Edmonton, Alberta
Posts: 31
If it's the same as the 2006, I believe it should be 05017479AA according to this website: http://www.scribd.com/doc/35523269/2006-wk-parts-manual

Or you can check http://www.factorychryslerparts.com/ . I wouldn't recommend ordering your parts through them though. I ordered some parts and they didn't ship them for a full month and it was impossible to get a hold of them. I had to start a dispute on Paypal to get things going.

The last option is just calling the local Jeep dealership and asking them what the part # is.
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