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Jk Running Rough Will not idle after a couple minutes

752 Views 11 Replies 4 Participants Last post by  DTB760
My Girlfriend has a 2002 4x4 with the 3.7. She has had it parked in the garage since 2014 not running. A pervious boyfriend had changed the plugs and it quit a couple days after.
The Jeep currently starts but wont idle long then dies if the throttle is opened and rpm's are up to 1200 to 2000 it runs with a slight hickup every couple seconds.

So far I have done the following.
Installed a different battery that tests good
Drained the fuel
Changed the oil
Changed the air filter
Drained and filled the coolant
Put some 91 octane in along with a bottle of Heet
Resealed the plastic manifold "I could hear a leak from there"
Changed all the sparkplugs because I dont think they have ever been actually changed
Replaced all the Coils
Cleaned the TB and replaced the IAC
Fixed vacuum leaks from old cracked hoses
Replaced the Cam position sensor but the new Duralast one seems to not work at all I might exchanged for a different one tonight.

Right now I have no codes
The MAP sensor indicates 12.3 at idle and 8.0 at 2k. We are at about 4k altitude and it reads 13.0 when off.
I have tried to cap the three vacuum lines from the manifold and TB.
The TPS indicates 13% at idle and 75% at WOT

Thinking maybe the Crank Position sensor next. Any ideas?


Derrick
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repost the model year and engine size... reading - 2002, 3.7L IDK

How did you check codes?

How did you determine new CMP was not working?
 

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- your title says JK -
Jk Running Rough Will not idle after a couple minutes

A liberty is a KJ - likely a typo
ok a 2002 LIBERTY 3.7L
Basics first -
check fuel pressure - see attachment a convenient place to attach gauge.

Your scanner is showing NO codes?

Is the jeep idling at 1200 to 2000 rpm ? clear that up please im confused.
 

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@DTB760
So after you crack the throttle open and raise rpm's it stays running, dies left to it's own at normal target idle speed. First thing I'd do if it were in my shop is hook the scan tool up and make use of the IAC stepper feature that allows you to open and close the valve body to raise / lower idle range rpm's and keep an eye on the fuel trims.

That will tell you if the IAC is accepting inputs from the pcm properly, if not then you have to look at the 4 wire circuit back to the pcm. ~You did install the new IAC with the o-ring?

Without having a scan tool that can do that, you should ground the test lead of a meter set it to ohms and remove the harness connector at the IAC motor and probe all 4 of the circuits back to the pcm. They should all test nearly identical with the ignition off.

If you can do that test with a meter and report back I'll help you iron it out from there.
 

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Discussion Starter · #6 ·
- your title says JK -
Jk Running Rough Will not idle after a couple minutes

A liberty is a KJ - likely a typo
ok a 2002 LIBERTY 3.7L
Basics first -
check fuel pressure - see attachment a convenient place to attach gauge.

Your scanner is showing NO codes?

Is the jeep idling at 1200 to 2000 rpm ? clear that up please im confused.
 

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Discussion Starter · #7 ·
I was having issues accessing the page from my phone, on the computer now. I will get back on the Jeep this week. It will idle at 900 to 1000 on its own until it warms up then it dies. I am thinking at this point there are some deeper issues, the vacuum is nowhere near what it should be at idle reading 12.8 when ambient is 13.2 in addition there is a large amount of carbon buildup on the IAC and TB, I was attributing this to EGR but realized this year has no EGR. I am going to do a compression test this week and see what that looks like. I am thinking a bad valve seat or valve
 

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Discussion Starter · #9 ·
So 0 compression on #2. I have never seen 0 on a compression test. #2 issue was the 4 cylinder plugs were installed. Same store sold me the wrong plugs years later and they matched so I didnt think anything of it.
 

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Discussion Starter · #12 ·
Pulled the new #2 plug and it was smashed, pulled the head last night and it is full of metal from the seat and the piston is bad, might have a small hole in it. Not sure what to do at this point and what is worth doing. There are 8 Liberty's at the Pick And Pull that are the V6 3.7 and in the 2002-2006 range. My biggest concern is 7 of 8 have no body damage, meaning there must be another issue. I have three options, pull a used head and piston $120, swap with a used motor $300 or buy a rebuild for $2200.
 
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