adkdremn

I've had some ongoing problem with 98 ZJ for about the last 3-4 weeks and it's getting pretty frustrating....I'm about to give up on the thing, it does have 236K.
The first issue, after sitting for a weekend I would have to jump it to get it started. Nothing major, but I just want to give a history of how things started. This could be due to the battery, although it's only two years old and the alternator is only about a year old. I was mainly contributing to the extreme cold and sitting for a few days.
On one of these days after jumping it, I had major issues out of nowhere with shifting and idling speeds. It was not shifting properly at all and was running at like 3500 rpms at highway speeds. So with all those issues I thought transmission. I have a slow trans leak, so I checked, it was about a quart low, and I topped it off. This helped, but I still had some minor isssue. It started to shift better on highway, but not totally better. In driving gears, it idled properly, but in park or neutral is running about 2000 rpms. This issues came and went and were better some days than others, but at least it was driveable. One morning, it was about 2 degrees, it started fine, but when I hit the brakes at a stop sign it just shut off. A couple of these times when going up hill it was bucking and carrying on like crazy...this was just on occassion.
The final issue, after jumping it and getting it running...after it had driven fine the week before, and I drove it all weekend, it would just shut off as soon as I let my foot off the gas. I had to give it gas to get it started, held the pedal down to keep the RPMs up some, but as soon as I let off, it immediately shut down. So now it's sat for a week, and I need to get it running.
Any thoughts with all these symptoms on what it could be?? Computer issues? Fuel pump? I'm at a loss, frustrated and ready to give up on the thing!

dave1123

First of all, I would look at your throttle position sensor. Take it off and clean it or replace it. Then look at the vacuum hose to the MAP sensor for cracks. A cracked elbow or hose the the CCV valve can also cause idling problems. ANY vacuum leak can cause weird power problems. You may even have a leak in your power brake booster.

There is a temp sensor underneath the battery that tells the PCM to cut back the charging rate when the battery gets warm. It's probably shorted and causing the alternator to not charge the battery properly.

Your transmission it pretty tired at this point and needs some help. Try shifting to neutral after start-up and allowing the engine to warm the trans for a few minutes before driving away. This will allow the seals in the trans to pressurize and soften because the trans pump doesn't run in Park.