Rough Idle Help

[404Fel]

Been fighting a rough idle since I purchased my 06 TJ (4.0L 6MT) and am hoping for suggestions on how to proceed. Jeep has been to two mechanics recently and neither can figure it out. I'm experiencing a moderate shake at idle that smooths out with any throttle. No CELs and runs great when moving. Warm idle hovers around 650rpm. Turning on defroster or A/C also clears it up significantly (I believe due to slightly higher idle RPM). Running voltage hovers around 13.4-13.5V since I do not have the battery temp sensor.

So far I've replaced / checked the following:
- New Spark Plugs (XP985) - Changed twice
- New Coil Rail (Standard Blue Streak)
- Replaced All O2 Sensors (NTK)
- New Fuel Injectors (Precision Auto Injectors) - Changed twice (Fuel trims were originally rich, now normal)
- Added injector and fuel rail heat shielding (DEI)
- New IAC (Mopar)
- New TPS (Mopar)
- New MAP Sensor (Mopar)
- Cleaned Throttle Body
- Checked for vacuum leaks, none found (per both mechanics)
- Replaced entire EVAP system (Mopar)
- Replaced fuel pump (Bosch)
- Replaced battery (Interstate MTX-34)
- Replaced Alternator (Ohio Gen. 330A)
- Replaced idler pulley, tensioner and belt
- Big 7 wiring upgrade (sanded grounds to bare metal
- Checked engine compression (180psi +/- 5psi all 6 cylinders)
- Checked catalytic converter back pressure (no issues, per mechanic)
- Smoke tested exhaust, no leaks found (per mechanic)

I'm sure I missed a couple things, but I feel like I've replaced just about everything that could be the culprit. Any ideas?

 

[JKP]

I'm guessing you have a lot of carbon buildup from those compression numbers. 120- 150 PSI is normal per the FSM.

 

[404Fel]

I'm guessing you have a lot of carbon buildup from those compression numbers. 120- 150 PSI is normal per the FSM.

Quite possible, kind of strange since the Jeep only has 80K miles. It was definitely neglected by the previous owners though

 

[macleanflood]

Maybe Seafoam the engine? Get a can, pull the vacuum line off the brake booster and dip it in the bottle...modulate the throttle to keep it running.

Watch for any exhaust leaks, too!

-Mac

 

[404Fel]

Maybe Seafoam the engine? Get a can, pull the vacuum line off the brake booster and dip it in the bottle...modulate the throttle to keep it running.

Watch for any exhaust leaks, too!

-Mac

Thanks for the suggestion Mac. I've never tried Seafoam before, but I guess it's worth a shot at this point!

 

[404Fel]

Sprayed a can of seafoam top engine cleaner into the intake and followed up with a good Italian tune up. No change in the idle unfortunately. Any other ideas?

To give some more information, the moderately rough idle is persistent, but sometimes when I pull into my garage, it will idle very poorly for 5-10 seconds as if it’s going to die. Lights dim and the engine audibly knocks until the computer catches it and smooths out after a bit.

 

[JKP]

It's not one of the typical PCM issues, but the 06 has a junk PCM, so...

Mark @Wranglerfix can help determine if it might be the PCM.

 

[macleanflood]

Have you actually cleaned the IAC? The orifice in the throttle body? Not just replace the part?

Thread 'How to clean your IAC (Idle Air Controller) valve'

Jan 2, 2016

If you're experiencing idle issues on your Jeep Wrangler TJ the most likely culprit (and the first thing you should check) is your IAC (Idle Air Controller). Often times the IAC gets very gunked up causing the Jeep to idle improperly. A simple cleaning is usually all it takes to get it running as good as new.

If you end up needing to replace your IAC valve (they do fail on occasion), you can find the part numbers (and the links to purchase them on Amazon) below:

2005-2006 IAC Valve (Part # 4861552AC)
1997-2004 IAC Valve (Part # 4874373AB)

There is no need at all...

• Chris
• iac idle idle air controller idle valve
• Replies: 191
• Forum: TJ How-to Guides

• 

-Mac

 

[404Fel]

Have you actually cleaned the IAC? The orifice in the throttle body? Not just replace the part?

Thread 'How to clean your IAC (Idle Air Controller) valve'

Jan 2, 2016

If you're experiencing idle issues on your Jeep Wrangler TJ the most likely culprit (and the first thing you should check) is your IAC (Idle Air Controller). Often times the IAC gets very gunked up causing the Jeep to idle improperly. A simple cleaning is usually all it takes to get it running as good as new.

If you end up needing to replace your IAC valve (they do fail on occasion), you can find the part numbers (and the links to purchase them on Amazon) below:

2005-2006 IAC Valve (Part # 4861552AC)
1997-2004 IAC Valve (Part # 4874373AB)

There is no need at all...

• Chris
• iac idle idle air controller idle valve
• Replies: 191
• Forum: TJ How-to Guides

• 

-Mac

Yep, cleaned the orifice as best I could when I had the throttle body off for cleaning. I do remember it was a bit tricky due to the design but felt like it was pretty clean by the time I installed the new IAC. At this point I'm tempted to try a whole new throttle body but am skeptical that would make any difference.

 

[macleanflood]

At this point I'm tempted to try a whole new throttle body but am skeptical that would make any difference.

That and nobody makes a reputable throttle body.

There is a way to o-ring the throttle body. Maybe a smoke test is in order.

For that matter a lot of the "new" parts might be contributing to the problem.

-Mac

 

[404Fel]

That and nobody makes a reputable throttle body.

There is a way to o-ring the throttle body. Maybe a smoke test is in order.

For that matter a lot of the "new" parts might be contributing to the problem.

-Mac

Yeah unfortunately the huge amount of new parts I've thrown at it definitely complicate diagnostics. I tried to use OEM parts when available (or high quality aftermarkets when not) but agree I can't really be sure any of them were good even in new condition. The only parts that were 100% necessary were the front O2 sensors (fixed a CEL and bogging/stumbling) and EVAP components (fixed fuel fill issue and improved idle).

Regarding the smoke test, both mechanics I took it to claimed to have performed smoke tests and noted no vacuum leaks. My understanding is that a leak should also increase my idle RPM, right? Once warm, it is very stable at 650rpm (with A/C off).

 

[macleanflood]

Regarding the smoke test, both mechanics I took it to claimed to have performed smoke tests and noted no vacuum leaks. My understanding is that a leak should also increase my idle RPM, right? Once warm, it is very stable at 650rpm (with A/C off).

I've never seen a TJ that didn't leak from the throttle body. Whether that is consequentially or not... here's mine...I replaced the throttle body gasket plus proper torque and it improved...I probably need to o-ring mine but zero idle issues so I'm not fixing what ain't broken.

-Mac

 

[404Fel]

I've never seen a TJ that didn't leak from the throttle body. Whether that is consequentially or not... here's mine...I replaced the throttle body gasket plus proper torque and it improved...I probably need to o-ring mine but zero idle issues so I'm not fixing what ain't broken.

I have heard they’re prone to leaks, but had previously ruled it out due to the normal idle RPM and both mechanics being adamant with their smoke test results. Thinking about it more, I do really wonder about both my replacement IAC valve and the port it sits into in the throttle body.

I can get a deal on a new BBK throttle body, which would help rule out any obstruction in the IAC inlet. Tempted to go that route and o-ring the new TB if necessary. If all else fails, I know I can adjust idle RPM up slightly with HP Tuners. Just want to fix any potential issue before I do a bandaid fix like that unless I’m truly out of alternatives.

 

[JKP]

No idea if it would cause your problem, but have you verified the CCV orifice in the rear elbow isn't clogged?

 

[JKP]

Also, have you looked for pending codes when it acts up?

 

[404Fel]

Also, have you looked for pending codes when it acts up?

I forgot to mention that I replaced both the front and rear CCV orifices and their seals and tubes due to oil weeping last summer, idle was same before and after. Good idea though!

No pending codes unfortunately and the CEL never even flashes when it runs rough. I did have codes for running rich but that was due to precision auto injectors mistakenly sending me higher flow injectors. Swapped them again for OEM sized injectors and fuel trims went back to normal, no more CELS.

 

[JKP]

Ok, I remembered somebody was having a screwy issue like this and it was either the cam or crank sensor. The 06 will run on only the cam or only the crank sensor. So, disconnect one and see if it fixes it. If not, reconnect it and disconnect the other one. It will take a long crank to start, and of course you will get a code, and be in limp mode.

 

[404Fel]

Ok, I remembered somebody was having a screwy issue like this and it was either the cam or crank sensor. The 06 will run on only the cam or only the crank sensor. So, disconnect one and see if it fixes it. If not, reconnect it and disconnect the other one. It will take a long crank to start, and of course you will get a code, and be in limp mode.

I can definitely give that a shot. I did note when I had a scan tool plugged in that the cam / crank difference was 0.4%, so theoretically well within spec. Guess that doesn’t mean I can rule them out though, right?

Edit: is this the thread you mentioned? https://wranglertjforum.com/threads...e-issue-cant-find-info-on-this-anywhere.7008/

His symptoms sound nearly identical to mine and it turned out to be his cam position sensor. I know the Mopar sensors are unobtainable now, so that makes it tricky if that’s my issue

 

[JKP]

It was more recent than that.

I've had a Dorman OPDA in mine for about 170K mi now, no issues. I think the NAPA sensor others have gotten to work is mad by Dorman.

If you have the OEM OPDA that needs to be checked for binding, gear wear.

 

[404Fel]

It was more recent than that.

I've had a Dorman OPDA in mine for about 170K mi now, no issues. I think the NAPA sensor others have gotten to work is mad by Dorman.

If you have the OEM OPDA that needs to be checked for binding, gear wear.

I do have the OEM OPDA. I’ve got a Crown replacement I’ve been meaning to swap in. Might try it with the Crown cam position sensor and see if that makes an improvement.