bp01

I have been reading other threads trying to string together the right terms to find others who have had this problem, but haven't been able to.

My 99 XJ 4wd Auto 109k miles which I got a few months ago has had this occurence two times so far. Both times after sitting in the parking lot at work all day I back out of my spot put it in Drive and go to take off. The engine revs as normal, but I get very little forward acceleration. As if something is not engaging completely. Eventually after 15 secs or so I hear a small clank sound which appears to be under my feet and then acceleration gets better. Once I get to the next stop sign. The problem starts all over and then eventually acceleration returns. After about 3 or 4 times everything is good to go and I drive home as normal no other issues.

Yesterday when this happened though I almsot think the Jeep went into limp mode after I heard the clank. When trying to accelerate the Jeep would hit ~2200rpm and then shutter a bit and rpm would drop back down. Idle was a little rough as well. I turned around before I hit the main highway and went back to work to jump underneath to see if I could find anything. The Jeep acted normal, I am no mechanic so I didn't find anything underneath. the 35 minute drive home showed no issues what so ever.

I am not positive, but I beleive this may be happening to a lesser extent more often, but it comes out of it so quickly that I can't really tell.

I put a 3" spring lift on a couple months ago as well. No vibrations or issues that I know of from that. I have always thought since I bought the Jeep that it had alot of front end noise, but its 13yrs old and a Jeep so I passed it off as a Jeep thing.

Any ideas on what could be causing this? It doesn't appear to be engine or sensor related because I hear the clank when things try to engage again. Not sure if this issue could have caused the Jeep to go into limp mode or if that was a completely unrelated issue. The engine always runs, starts, idles well.

Bustedback

Have you checked the transmission fluid level?

bp01

Transmission fluid level actually appears to be a little over max ideling in neutral. It is red, but does have a used smell to it. I would say a new filter and fluid would be a good idea, but I do not believe it is in poor enough condition to cause this. I could be wrong though.

bp01

I drained the tranny fluid this weekend. It was pretty dark stuff. Looked more brown than red. Smelled well used as well. I also put in about 1/2 qt less than I drained out. It is now showing right in the middle of the operating range on the dip stick. I plan to run it this week and then drain the fluid again and replace the filter. There did not appear to be a bunch of stuff on the drain plug or in the drained fluid. Drove it around right after the fluid change and everything seemed fine.

Jumped in it on Sunday got a 1/2 mile down the road and the engine started stuttering / missing out slightly at 55mph. Couldn't hold 60mph. RPM kept jumping around. Almost turned around, but it came out of it an ran good the rest of the 20 min trip.

Left the Jeep parked for 3 hours and then got back in to come home. Turned over longer than usual started for a second and then died. Tried starting it again and it started a little rough but then came out of it an ran great all the way home.

Drove it to work this morning and ran like a champ. Not sure what is going on, but I now beleive the slipping / clank was unrelated to this engine issue.

I am thinking clogged fuel system or a sensor going out. I am just guessing though. Shouldn't my check light have come on though if it was stuttering like that? Where do you guys think I should start troubleshooting?

Bustedback

It should, but it sounds more like a fuel pump problem than a transmission problem.

bp01

That is the direction I was thinking as well, but trying to link it all together though could it be a vacuum problem? I definetely hear a faint whistle sound under the hood when a let off the gas. This could cause the engine to run poorly, the solenoid in the transmission and the torque converter to not function correctly right?

When I tried to turn the A/C on yesterday it wouldn't change from defrost to vents. It kind of got stuck in the middle and it was like all the air was trying to push out of a really small resitricted hole. It eventually made a small thud and then the vents opened up. This runs off vacuum as well right? Could all of this be interconnected?

How do I diagnose and fix a vacuum problem. What does the vacuum system even look like or consist of on an XJ?

Bustedback

You have a vacuum leak someplace. Spray the vacuum lines with carb cleaner while the engine is running and listen for the idle to change once you find the leak.