1991 XJ, 4.0, Automatic, 4x4

Runs like a top most of the time, but occasionally (and randomly) idles so low that it eventually stalls. At the same time, it seems to be down on power and the auto shift points in "Comfort Mode" seem high (I suspect because I need more throttle to accelerate with traffic). It's either all of the symptoms or none at all. It either runs great, or idles like junk and is a little down on power. Not way down on power, just a little. No CEL. The indicated battery voltage is normal in all conditions, too. It drops a tiny bit at idle, but still nowhere near the low end of the gauge.

In addition, I had the intake manifold off to install a new header a few weeks ago and noticed that there was a lot of fuel on the floors of the runners. Is that normal? I pulled the intake manifold after cold-starting it and pulling it into the garage, then immediately shutting it off. By the way, the idle/power problem was not affected by the header swap.

It always seems to start and idle normal-ish when cold. Cold idle is an indicated 700 or so (which I assume is ok).

What do the gurus think? Where should I start? I really want to go camping this weekend, but if this machine isn't running well, I may have to take my Honduh (which hates camping). Halp!

 

Welp, if anyone ever encounters the problems I described above and cares how I fixed it: The coolant temp sensor was damaged and the vacuum line to the fuel pressure regulator was leaking. I replaced the coil too, for good measure (it was stumbling a little at low RPM/high load). Fixed those three things and it runs like a champ. I'm interested to see if my fuel economy improves now...

 

1991, it's 23 years old, it wouldn't hurt to replace all the vacuum and rubber fuel lines.