So my roommate got a 99 XJ 2 Dr 4.0 5 speed 231 t-case with 125k last week, runs great no issues other then rust. It has ran great for him this past week, then tonight he left the interior light on for a few hours, and wouldn't start, no biggie we jumped it and it died right away. Tried again same thing.. So we got it started but as soon as he lets go of the gas it would die.. So he gave it a little gas about 1000-1500 rpms and ran it for about 5 minutes to get up to temp and still it would want to die out.. He drove it around the block for another 5 minutes, and then it just magically idle fine??

Any ideas on where to start?
It has newer plugs, the PO also said he did the wires cap and rotor about 20k ago, not sure if its true since they look older.. Battery does looks a little older, but has fired right up for him without a slight hesitation up til this point.
Also battery terminals look pretty clean and tight.
And it does have a working gas gauge, and has a half tank at the moment.

 

Pull the Idle Air Control valve, spray it with carb cleaner, scrub it with an old toothbrush, and pop it back in. Should only take 10 or so minutes. That's my first guess with your issue.

 

Thanks, I will be sure to let know, and to tell him to clean the entire TB while hes in there.

Strange twist, it started right up this morning and idled as it should have..

 

Good call on that. Interesting... Automobiles in general like to do that though, have intermittent issues. Like one day it'll run terribly and the next day it'll run like it's brand new.

Cleaning the TB and IAC are easy and probably free to do, unless you don't have a can of cleaner laying around. And if it doesn't fix the issue, you just rooted out a couple likely suspects.

 

Well I guess all day it ran great, even with the temps down to about 30-35 today, it started right up..
Will still be cleaning the IAC and TB this weekend though.