My 2000 XJ just started to have erractic idle and randomly will cut-off. I've replaced Idle air control vavle, battery, spark plugs, air-filter (not that it would really matter, just sayin though) and cleaned my throttle body (which helped)

but the problem still hasn't gone away, thinkin maybe the coil rail? any ideas?

 

Maybe your MAF is going out, thats what it did on mine.

 

yeah I guess that would make sense, cause highway driving doesn't show any loss of performance.

 

Have you checked for codes? Even though no CEL is on there still may be Code(s) stored any big box parts store will do this for free. No need in taking random guesses at it, as all this does is cost you $$.

You should try to get a manual Factory Service Man. is best, or Chiltons, in pinch Haynes will work. This will have the troubleshooting guides that will let you to systematicly work your way to a solution effeciently.

You said you you replaced the battery, was any attention given to the connections? There are 3 grounds in the engine bay, the one that goes from the the head to the firewall (braided wire) is well known for corrosion. This should be done (electrical connection inspection/Replacement) after having it scanned for codes but before any further steps are taken. post any codes found.

 

You mean MAP sensor?

 

You can manually check your for codes also. On-off thing.

 

No, the mass air flow sensor.

 

I did check all my grounds and cleaned everything up.

I haven't checked for codes though, I have my own Matco scan tool that I use at work so i'll do that later today.

I noticed if I would stab the gas (press it to the floor and completly let-off) then when the RPMs would drop it would just shut-off like someone turned the key.

 

Is your xj the 6 cylinder?

 

Also I forgot, check fuel pressure it should be 49psi +/- 5 psi @ idle

 

yeah i've got the 6 cyl. feel kinda dumb now for not adding that to beggin with lol.

haven't checked the fuel pressure yet but preciate the specs, i'll be sure to do that when i get it back to work.