06 jeep liberty rough idle

Bowtiecrazz · **Joined:** Mon Dec 12, 2022 7:51 am **Posts:** 19

So the jeep idles good when first started. Runs good down the road. Idles good in gear but after it warms up it idles rough in park or neutral. Tap the throttle a little bit it smooths out. Put it in gear it smooths out. Already did the intank pump upgrade.
Only code is p1252 I switched the vacuum lines waiting on the sensor to come in. But still not sure what is going on with the idle problem. Any help would be greatly appreciated
Fuel pressure at idle in park is 5935.7

WWDiesel · **Posted:** Mon Jan 16, 2023 12:11 pm

Bowtiecrazz wrote:

So the jeep idles good when first started. Runs good down the road. Idles good in gear but after it warms up it idles rough in park or neutral. Tap the throttle a little bit it smooths out. Put it in gear it smooths out. Already did the intank pump upgrade.
Only code is p1252 I switched the vacuum lines waiting on the sensor to come in. But still not sure what is going on with the idle problem. Any help would be greatly appreciated
Fuel pressure at idle in park is 5935.7

Could be your serpentine belt tensioner pulley has gotten weak and allowing the serpentine belt and pulley to bounce at idle.
If the alternator override pulley is bad, it can contribute greatly to the belt and tensioner pulley bounce due to the odd pulsations of the 4 cylinder engine at idle.
To test, simply remove the serpentine belt after the engine is up to normal operating temperature, start the engine, and see if the rough idle goes away.

Note; if you hear a rattling noise at idle, it is the engine mounts, they are hydraulic and when worn out can emit a rattling sound especially at idle when the engine bounces most due to the pulsations. :wink:

Bowtiecrazz · **Joined:** Mon Dec 12, 2022 7:51 am **Posts:** 19

Not sure if you can here it but this is what it sounds like.https://youtube.com/shorts/VHtlErvjbC8?feature=share

Bowtiecrazz · **Joined:** Mon Dec 12, 2022 7:51 am **Posts:** 19

The part where the engine smooths out is when I put it in gear

jws84_02 · **Posted:** Mon Jan 16, 2023 8:54 pm

Hard to tell from that video. Better if it was video with the hood up and camera looking into the engine bay. How many miles are on it? It could be rockers starting to fail

Bowtiecrazz · **Joined:** Mon Dec 12, 2022 7:51 am **Posts:** 19

Let me know if this is any better. Thank you
https://youtube.com/shorts/hhuG9NVlQ7k?feature=share

WWDiesel · **Posted:** Thu Jan 19, 2023 1:09 pm

Bowtiecrazz wrote:

Let me know if this is any better. Thank you
https://youtube.com/shorts/hhuG9NVlQ7k?feature=share

Much better video!
Your tensioner pulley looks like it is bouncing quite a bit.
Have you ever replaced the alternator override pulley?
When they freeze up, they can cause the engine loping at idle and the bouncing of the serpentine belt/tensioner pulley.
Also, the tensioner pulley tension spring can get weak with age and should be replaced. :wink:

jws84_02 · **Posted:** Thu Jan 19, 2023 7:08 pm

Holy crap. That tensioner is dancing pretty good. Alt decoupler is probably shot. And I don’t know if William heard it but close to the beginning it sounded like maybe the crank dampener is starting to fail. But I’m not sure on that one, it could be my phone playing tricks on me

WWDiesel · **Posted:** Thu Jan 19, 2023 8:51 pm

jws84_02 wrote:

Holy crap. That tensioner is dancing pretty good. Alt decoupler is probably shot. And I don’t know if William heard it but close to the beginning it sounded like maybe the crank dampener is starting to fail. But I’m not sure on that one, it could be my phone playing tricks on me

It is hard to say jws84_02, I re-listened to the video several times, but can't be sure on the harmonic balancer. I did notice what little the video showed it, it seems like the balancer pulley is wobbling quite a bit which might be an good indication of the balancer pulley is failing. ???

A very simple test: Remove the serpentine belt, start the engine and listen and to hear what noises disappear. Also observe the crankshaft balancer pulley closely while the engine is running with no belt on it and see how bad it is wobbling.
With the serpentine belt removed (engine OFF), manually grab the harmonic balancer pulley by hand and try to wiggle it and see if it is loose or has any obvious play in it.

Bowtiecrazz · **Joined:** Mon Dec 12, 2022 7:51 am **Posts:** 19

Appreciate everyone's input, I'll try getting the belt off tomorrow and checking the noises out. Is there a easy way to test the alternator decoupler ?
Thanks again everyone

WWDiesel · **Posted:** Fri Jan 20, 2023 3:29 pm

Bowtiecrazz wrote:

Appreciate everyone's input, I'll try getting the belt off tomorrow and checking the noises out. Is there a easy way to test the alternator decoupler ?
Thanks again everyone

With the serpentine belt removed (engine OFF) very carefully insert a small screwdriver into one of the slots in the front of the alternator into the cooling fan blades to hold the rotor stationary.
Then grab the OAD pulley by hand and see if the pulley will rotate freely in one direction but will not rotate in the opposite direction. If the pulley will not rotate freely in one direction, the pulley is froze up and should be replaced. :dead:

Note: If you see red dust coming from the plastic cap on the front of the pulley, that is usually a good indication that the pulley is bad.

taroo · **Joined:** Sun Apr 27, 2008 2:14 pm **Posts:** 276

IDparts has the alternator pulley on a clearance sale now.

I have replaced two on my 05 CRD.

06 jeep liberty rough idle

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