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Hesitating idle ??

Pharaoh XJ

NAXJA Forum User
Location
Cairo, EGYPT
I recently had to change the freeze plugs on my 1994 4.0 auto, Had to take off intake/exhaust manifolds for the install.

After putting everything back together I started the engine hesitated a bit at first then it stabilized.

Then later after I drove it for a long drive was going fine, went to the store then came back out the engine idle really low revs then went back up. the revs kept paying from low to high, when I drove it, it didnt want to go over 2000 revs, then suddenly goes past it.

It stays like that for 10 mins then everything is back to normal, its done it three time in 4 trips.

btw : it threw codes
52: O2 detects rich mixture. Check fuel injection system and sensor.


although I dont have an O2 sensor --> leaded fuel ECM

&
12 : Battery or power to the ECM disconnected in the last 50 key cycles.


Any ideas ??
 
Sounds like it could be an intake vacuum leak that seals as the motor warms up. Try starting it when it's cold and spray carb cleaner on all the intake to head joints. If the RPM suddenly changes, you've found where it's leaking. Did you disconnec tthe battery when you took the manifolds off? That would be the code 12. The vacuum leak could cause the code 52.
 
Yes I disconnected the battery
can this vaccum leak be from one of the hoses or from the gasket

Hose = constant problem.

Gasket/manifold = can go away when heats up.
 
I recently had to change the freeze plugs on my 1994 4.0 auto, Had to take off intake/exhaust manifolds for the install.

After putting everything back together I started the engine hesitated a bit at first then it stabilized.

Then later after I drove it for a long drive was going fine, went to the store then came back out the engine idle really low revs then went back up. the revs kept paying from low to high, when I drove it, it didnt want to go over 2000 revs, then suddenly goes past it.

It stays like that for 10 mins then everything is back to normal, its done it three time in 4 trips.

btw : it threw codes
52: O2 detects rich mixture. Check fuel injection system and sensor.


although I dont have an O2 sensor --> leaded fuel ECM

&
12 : Battery or power to the ECM disconnected in the last 50 key cycles.


Any ideas ??

Hi did you get the problem fix on your Jeep?, I am having the same exact problem on my euro-XJ. I also have the leaded fuel ECM. I did the same job like yourself, pulled out the intake and exhaust manifolds and now my RPM's goes up and down randomly, but once it stops it goes away for good. I installed a brand new gasket a month ago but I reused yesterday since it looked in mint condition when I performed this other job. HELP!

I do have the 52 DTC too ,

'94 Export XJ (Manual) .

Thanks
 
Last edited:
UPDATE:
I replaced the intake/exhaust gasket & made sure that I installed it correctly as it can be installed om both faces but only one is right & its is stamped on the gasket

The problem was a vacuum leak causing the bad idle
 
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