View Full Version : stumbles once after hot soak??

July 28th, 2007, 20:33
My 98 has been doing this for awhile, and I am getting sick of not knowing what is causing it.

After a hot soak my xj will fall on its face for a few seconds then accelerate like normal. This happens usually when I am home for lunch and heading back to work, just as I am pulling out of my driveway and accelerating down the street. Sometimes if isn't as bad as others, but noticable. I once had what seemed like a backfire through the t-body.

I have tested most of the sensors (tps, cts, iat) and/or swapped them out (map, tps, O2, IAC), and check fuel pressure (no bleed down, normal pressure). I get no check engine light, and no stored codes. Being intermitant I really haven't gotten any results, but i assume it isn't one of the swapped sensors.

This doesn't sound like the vapor lock common on the 99-00 xj's to me, but I guess it could be.

Any ideas?


July 29th, 2007, 07:23
I am having the same problem with my 98. Never used to do it, seems like it just started this summer.It's usually if i get it to operating temp, then park it for 10-30 mins, then drive it again, it hesitates just for a second when I get on the gas, then completely normal. I was wondering about heatsoak, too. Maybe the 98s are better insulated then the 99+, but as the insulation ages it's not as effective?

July 29th, 2007, 08:20
Mine's doing the same thing, but I also have some bucking/hesitation issues under full throttle after it's been driven long enough to get good and warm.

July 29th, 2007, 12:26
I have a 98 and i am having some similar problems. After a hot soak it will stumble then act normal again ect. Mine actually starts running weird at idle durring normal driving like in heavy traffic and stuff. It was doing it when i got to work one time and i work at a shop so i grabbed a fuel pressure guage and hooked it up. I did a volume test and all that came out was vapor... I had another guy look at it and he said it needed a fuel pump so its on order right now.... i will let you know if that is the fix.

July 30th, 2007, 11:53
please let me know. It seems like alot of people have this, or very similar problem.

I will try to hook up my fuel pressure guage and monitor the pressure over this weekend.

Matthew Currie
July 30th, 2007, 13:36
My 99 has just started getting a rough idle briefly after a hot soak. I haven't had time to analyze it. No codes, and no problems running otherwise. My next step will be to run some techron or something through it, in hope that it's a dirty injector.