I just put a new 4.0 in my 93 xj and have put 2000 miles on it and here recently when I start ot up it will die down to about 500rmps then rev itself up about three times then idle normal for a cuple seconds then almost die agien. It will do this the whole.time its sitting and idling then when I drive it it still wants to die even at half throttle but will pick back up. After about 10 miles of driving tho it clears up and does good till I cut it off and start it back then it will do it agien. Any ideas ?

 

A new 4.0!? The last remaining, unused, new 4.0?
Or did you steel CCKen's man-cave signed anniversary ashtray-4.0?

 

Sorry I mean a remaned 4.0 from napa lol new to me

 

Check if any codes are present .

 

Sounds like its searching for the right AF mix- check your oxy sensor.
http://www.naxja.org/forum/showthrea...en+sensor+test
How's your mpg?

 

Ideas? Yes, several things can be going on...

Checking for codes is always a good start with any issue. For the simple reason that it's might give you the lead towards the solution.

Have you done any testing yet? Or cleaning?

 

no codes cleaned throttle body, and idle air, checked all vacume lines,checked fuel pressure thats as far as I have gotten so far.

 

Oxygen sensor.

 

Wounder if a 89 and 93 o2 sensors are the same? I need to p9ok it up if so ill pull the one outa my 89 and see how it acts. Money is kinda tight right now so wanna try to pin point it befor I go spendin money. Thanks for the advice ill post updates here in a few.

 

Well I pulled the wire loom back on the o2 sensor and one of the wires is broke off the sensor so looks like im gona get a new one and see how it does. Thanks for all the info ill post updates ones I get the new sensor.

 

The 02 sebsor fixed it thanks guys.