4.0 surging at idle

[05 White X]

05 4.0 auto with reman engine when I got it. It has a slight surge at idle and coasting @20-40rpms. I have changed all sensors and vacuum lines, engine only has @ 800 miles on it. Anybody have a 05 or 06 experience this and have any ideas.

 

[IJK]

is the A/C on or off? Check and clean the idle air control valve.

 

[05 White X]

A/C doesn't matter and have put 3 new icv's in it. 2 mopars and one standard no differance along with new throttle body.

 

[taylormade73]

Did you replace the TPS with a Mopar one?

 

[IJK]

A/C doesn't matter and have put 3 new icv's in it. 2 mopars and one standard no difference along with new throttle body.

The surging is likely the PCM trying to maintain the idle AF ratio of 14.7 as factory programmed. To do this the PCM monitors the two upstream O2 sensors. Both intake air leaks and exhaust leaks can cause surging. Exhaust leaks both upstream and downstream of the O2 sensor are often overlooked. Even small exhaust leaks close to the O2 sensor can have a major effect of the sensed AF ratio.

I am sure you already know this but it often missed, only use NGK O2 sensors.

 

[05 White X]

Did you replace the TPS with a Mopar one?

yep

 

[05 White X]

The surging is likely the PCM trying to maintain the idle AF ratio of 14.7 as factory programmed. To do this the PCM monitors the two upstream O2 sensors. Both intake air leaks and exhaust leaks can cause surging. Exhaust leaks both upstream and downstream of the O2 sensor are often overlooked. Even small exhaust leaks close to the O2 sensor can have a major effect of the sensed AF ratio.

I am sure you already know this but it often missed, only use NGK O2 sensors.

O2 sensors are ngk and exhaust is new also, I have three of them one which is a wranglerfix. no difference. No leaks noticed

 

[IJK]

O2 sensors are ngk and exhaust is new also, I have three of them one which is a wranglerfix. no difference. No leaks noticed

Wow, you must have fortune invested.

O2 sensors are ngk and exhaust is new also, I have three of them one which is a wranglerfix. no difference. No leaks noticed

Does your TJ surge in neutral?

 

[05 White X]

LOL not much that hasn't been replaced or rebuilt. and yes in neutral or park @ 20-40rpms shows on code reader

 

[Daryl]

With the engine running spray carburetor cleaner where the intake manifold bolts to the head. If the idle rises, you have a leak.

 

[IJK]

Wow, you must have fortune invested.


Does your TJ surge in neutral?

LOL not much that hasn't been replaced or rebuilt. and yes in neutral or park @ 20-40rpms shows on code reader

Did you rebuild the transmission when you did the engine?

 

[05 White X]

With the engine running spray carburetor cleaner where the intake manifold bolts to the head. If the idle rises, you have a leak.

Used brake cleaner and no leaks a few times

 

[05 White X]

Did you rebuild the transmission when you did the engine?

Trans was already done by a PO

 

[LONGJP2]

Used brake cleaner and no leaks a few times

Wasn't non-flammable, was it?

 

[05 White X]

Didn't know there was non flame able brake cleaner so no

 

[LONGJP2]

Didn't know there was non flame able brake cleaner so no

 

[05 White X]

Ok so I don't use that stuff, only the good flameable stuff.