MJ hesitation while cold

Hey guys, I've been a long time user of this forum, and have been a member off and on. I've had a couple XJs, and just pick up an 88 MJ. It is 2wd, 4L, w/ speed, just under 170K. My question is concerning a hesitation, or stuttering until it gets warmed up. Under accelaration, until you drive about 5 miles, it will stutter/hesitate occassionally. The previous owner replaced: cap/rotor, wires, and coil. Once warm, there my be a very mild hesitation, but hardly noticable. It runs very strong other than that. What sensor should I be looking for, or could it be something else entirely? Any direction would be helpful. Thanks in advance.

Could be a few things. First off, do the ground refreshing and C101 refreshing.

Click on the link below and do the simple things outlined in posts 1,2,and 3.

We can go from there.
http://www.jeepforum.com/forum/f140/cruisers-mostly-renix-tips-1304879/

clean all grounds. test/replace o2 sensor, coolant temp sensor, TPS, CPS, and also Id pesonally go through and do cap/rotor/wires/fuel filter/air filter and check all vacuum lines and exhuast leaks just to make sure I am starting fresh. Id also run some sea foam through the intake before I changed the plugs and oil.

Id put a multimeter on the TPS and test that. consider grabbing some ford 19lb injectors.
check fuel pressure? how are the battery terminal connections?

once again, go nuts on the grounds, and clean up the c101.

basically rule out all of the cheap obvious easy stuff, and give yourseld a major tuneup at the same time.

All of the above and also make sure that the plastic vacuum line going from the TB to the MAP is in good shape. I have had one to crack and when the motor would rock on acceleration, the vacuum line would open to atmosphere and the engine would stumble.

Thanks for all of the replies. Now I just need to make the time to start trying them. I will work on that, and post an update, hopefully soon.

Update on this issue. I adjusted the TPS, checked IAC valve, tested MAP sensor voltage, checked the grounds, and cleaned the C101. Still no improvement. I have noticed though, the hesitation occurs in a narrow rpm range. Example, from a stop, everything is fine until a certain rpm is reached,(maybe a little over 2K, no tach) and it starts bucking, and maybe a backfire. if I let off, it immediately goes away, or if I put the pedal down, it if fine. Same thing cruising, most of the time it's fine, but if I'm in that certain rpm range, it misses/hesitates. Still seems to be worse when cold, but does it in this cold weather pretty consistently. Any idea why it's only in a narrow rpm range??

xjtrailrider said:

All of the above and also make sure that the plastic vacuum line going from the TB to the MAP is in good shape. I have had one to crack and when the motor would rock on acceleration, the vacuum line would open to atmosphere and the engine would stumble.

Click to expand...

THIS! Check this first!

next, pull the vacuum line that feeds the reservoir and plug it, test drive.

definitely sounds like a vacuum leak issue, I think it would be worth getting a vacuum gauge before you waste a dime on sensors.

Will do, thanks! Would be really awesome if it were something so simple. I'll check it out tonight. Runs like a dream other than this issue.

Could be a bad spot in the tPS also.

I checked the hard line from TB to MAP. Looks good. I unhooked it to see how it ran, and it barely stayed running. Pretty confident that line is OK. I'll look for a TPS to try and see what happens.

Cheap XJ, I have to say, you might be onto something. The line itself is ok, but maybe was leaking around the fitting on the MAP sensor. I disconnected it from there, and put it back on last night. Drove it to work today, and it had a very slight hesitation at times, but seemed to be better. I'll keep driving it, and see what happens. Thanks for the idea!