96 xj rough idle( winded explaination )

I have a 1996 XJ 4.0, a/c,automatic.
I have been working out some cooling issues and have come across a situation never before encountered.
With the hood open and the a/c on or off the Jeep idles fine and the gauge temp remains within range.
However with the hood closed and the a/c off within a minute of the aux electric fan coming on I experience a rough idle. Also if the hood is closed aux fan is off and I turn on the a/c the same thing happens.
I also notice that there is a sound coming from the air filter box that sounds like it is starving for air. My filter box has a rectangular "intake" hole that is open to the engine compartment.
My thought, call me crazy or uninformed, but would the hot air coming off the radiator and a/c condensor have this effect?
This only became an issue since the radiator was removed as well as the replacement of all the cooling components.
Any thoughts, suggestions, or "I had that too" will be appreciated and accepted without question.:helpme:

I had that same problem, not really but you wanted somebody to say that, It sounds like a Jeep trying to tell you it's needing to go wheelin. Take the air filter out and try it again. Is it plugged up? It's sounds like it's loading up or leaning out when the aux fan kicks in- no ideas.

Take off the throttle body, then take off the idle motor on the side. Clean it (as well as the TB itself) with carb cleaner. Put it all back, and RESET THE COMPUTER! (I.e. disconnect the battery - for 10-15 minutes).

Just a suggestion, this worked for me!

I'll also explain why I think it will work. In my case, after swapping in a '93 4,0 from a ZJ, I had connected the MAP sensor to the wrong wires, i.e. the computer got no information about manifold vacuum. It somehow "learned" to run and idle by using the rest of the sensors, as well the idler motor. I first suspected the idler motor was clogged up, as I had been tipped about, and after cleaning it the engine idled way too fast. When I finally found the mistake and connected everything the way it was supposed to, it still ran weird... after resetting the computer, it had to "relearn" everything. I recommend resetting it every time you change a sensor, correct any mistakes (like vacuum leaks etc.) or clean the RB and idler motor, because the computer "gets used to" the flaws, and adjusts gas and ignition to it, so that when you correct it it runs incorrectly again. After resetting it it idles rough for a while, maybe it will stall at first, but keep trying to start it without throttle and it will wake up and smell the roses... very cool, my very own Terminator under the hood!

Oh, one more reason why you should reset the computer: It controls the idle according to what accessories are running, i.e. it gives more throttle when in gear or probably when the fan is drawing current, to keep the idle steady.

willysnut said:

I had that same problem, not really but you wanted somebody to say that, It sounds like a Jeep trying to tell you it's needing to go wheelin. Take the air filter out and try it again. Is it plugged up? It's sounds like it's loading up or leaning out when the aux fan kicks in- no ideas.

Click to expand...

I think it needs some wheelin time too.
I use a K&N filter, pulled it and put in the stock one with no change.