For the past couple days, my '99 TJ Sport 5-speed (156K+ miles) has been acting up. The main symptom was not being able to hold an idle, however there has been a slow oil leak from the aft end of the engine and a pretty bad leak into the passenger side floorboard and under the core also (heater core issues, I presume). The engine would crank OK, but without holding the accelerator open, the engine would bog down and stall, but at higher RPM (1000+), it would run normally. Once I had run it for a bit (25 minute highway ride to work), the symptoms would disappear on their own. However, after work, they would return but again be gone by the time I got off the highway on the way home. This morning went the same way, but this afternoon, the symptoms remained after the highway trip home (problem getting worse).
After a bit of searching the forum, I decided to get some throttle body cleaner and see if that would help. Took the TB off and cleaned thoroughly, then re-installed and poof: symptoms gone. I am curious as to how it will act in the morning after sitting overnight, but it did seem to crank a little faster, and throttle response seems to be a bit better (only sitting in neutral in the driveway). I also added a bottle of Lucas fuel injector cleaner to the gas tank (they were on sale and I figured it couldn't hurt).
While I was watching/listening to the engine run after the work was done, I thought a couple of the valve cover bolts (forward driver side) looked loose, so I checked and was able to tighten most of them by hand with little effort (some at least a full turn). I tightened everything (no torque wrench - dinner was ready...), but think I have figured out where the oil drip has been coming from. I previously thought it was the rear main seal, but I think this was a good find.
Plans for the next couple weeks (I will be offshore for work for a few days the rest of this month) include checking/fixing spark plug gaps (or replacing if needed), new valve cover gasket and securing cover with proper torque, new distributor cap and rotor, and some further research about the potential heater core issue. Any advice or thoughts would be greatly appreciated!!