THE ISSUE:
my 99 xj has this hesitation where, under light throttle, it will sorta backfire and run rough. it will only misfire, hesitate, call it what you will, untill you get the throttle open enough, then it runs normal.

THE FIRST STEP:
new cap/rotor, plugs/wires, blew out gas lines and cleaned the tank/pump assembly, visually had injectors checked, tested fuel pressure.



THE NEXT STEP:
(all by myself) new TPS, that didnt do it... so a new IAC valve, as i said, it will do this at a lower throttle, so this seemed logical... while doing my initial test drive aftet doing the IAC, there was SOME hesitation, but it cleared quickly.

all was well untill just today when after 5 miles, it started to act up like before i did any work. i dont know for sure that the fuel pump is always giving a steady amt. of pressure, but why did the problem go away, then come back??? did i not fix it, was it just dormant? i can still do the o2 sensor and coil, but i am about ready to give up on this... PLEASE HELP!!!!

 

02 sensors make the most sense to me. is it throwing a check engine light?

 

See if you can borrow or if you have one do a compression test as low compression can cause this, it may need the valves regrinding if high mileage?

Stuart

 

haha.. the check engine light has been on since i bought it- there is a small leak in a vac line SOMEWHERE... not enough of an issue to effect the jeep, but enough to trip the light. so idk, its been pluged in a bunch, and it will clear for a few days, then start throwing same code again. so far it hasnt sais anything about the hesitation.

 

its got <90k, but idk if its actually been compression tested.. while changing plugs, we snapped one and had to move jeep out of shop. it ran pretty well on just 5.. but does this tell you anything about compression?

 

The vacuum leak could mess up the MAP sensor, which will cause hesitation.

I would fix that 1st

 

i was wondering if the computer was screwed up, either the ecu or map, any suggestions on where to get a new one.. the guys at Bond Auto know me by name now so id probably go there... OEM will be just fine... any thoughts on if i got a good deal, or got ripped off on this IAC?
http://www.autopartswarehouse.com/sk...%26+Drivetrain

 

throwing parts at a problems never fixes it unless your lucky.

What i would do is unplug the vaccuum line for the MAP and see if it changes.

Or remove all the unnecessary vacuum lines and cap them to see if it the MAP. You only need vacuum for the fuel rail, the brake booster (just a smart idea) and the MAP sensor, i think thats it, and see if the hesitation still persists

 

so far all the sensors, or plugs, when pulled effect the idle. but ill need some help (or a daigram) to know which lines to unplug. also, one time i was low on gas and put like $10 in, and pulling out of station, it hesitated. later in day, i topped off tank, and upon pulling out did it again... ugh...

and yea, my luck sucks, so i dond wanna waste the moneys... i dont mind doing preventitive work, or the like, but his is getting down to just the pricey parts; new pump/filter assembly is like $200....

 

i am leaving for a week, and ive heard the process of unhooking bat. leads and holding together for 30 sec... etc. but while im gone, should i just unplug the bat. and leave it off for the week? will it do anything???
if anybody feels like throwing humor into this thread, i could use it... total sad clown frown right now... i love my jeep, but she makes me want to cheat on her... silent rage, silent rage, you get the idea... thanks, peace.

 

Just a few words of advice... NEVER GIVE UP ON YOUR XJ!!!
Becuase i bet it would NEVER GIVE UP ON YOU!!

 

let the homor roll in!!!!!!!!!!
i already feel a little better!
oh, and BTDubs, i probably will never give up... my last car (93 saturn) cost me like an avg. of 400 a month for 4 months straight. but we were just reminising on how it would still do a good 50mph drift w/o ebreak... cant wait for snowy roads!!! im gonna tear it up... hell, even talking drifting is making me feel better... anybody got some good vids of their jeep drifts? id love to see em!!!

 

I cant wait for snow either. I usually pull people behind my jeep on sleds with a ski rope. So much fun. We also get everyone with 4x4 or 4wd together and find neighborhoods to go drifting in. In Flint, MI they only plow major roads so its a blast.

 

My 91 does this a little also, kinda shakes the body a little to? It also backfires a little when a little bit of gas is given. Anyways, Im replacing my exhuast system (I know MY jeep) and Im pretty sure that will take care of it. Didn't see any exhuast items on ur "already fixed", maybe check it out.

 

x2 on the o2 sensors (especially harness side of connector, search my threads, i've had this issue)and the vac leak.
Good luck!