Another YJ problem

My son was driving home during the storm and stopped at a stop sign, jeep stalled. Restarted but everytime he put it in D or R it instantly died. starts and idles fine but move it out of N or P and idle cuts out and it dies. Strapped it to a friends house and due to scheduling we have not been able to work on it yet. He did find one loose vac line from the weber conversion but thats about it. Any ideas, one consensus is water in the cap but I think that if that was the case it would have dried out after 20 min of idling. How does an automatic tranny interact/effect an engine. This YJ has had the nutter bypass which puts the computer to sleep so the computer I think is not part of the problem.
Info: 89YJ, 4.2, Weber, auto, tilt column and thats about it.

The '89 YJ used a Chrysler 904 tranny, didn't it? I thought that was a "dumb" tranny -- no TCU, just vacuum controls like in the old days. I doubt there is much interaction. Sounds more like something is affecting the engine so that it doesn't like to run under any load. Cracked distributor cap, perhaps?

904 or 999 tranny. He's looking at it now, me, I'm flushing my XJ, tstat, hoses and getting it ready for winter. Hope to see it roll into the driveway soon so we can do the radiator today as long as I have all my cooling system stuff out.

Here's an off-the-wall thought. Although the 904 is usually not computer controlled and in old AMC days did not usually have a lock-up torque converter, we are talking about AMC here. Bob Salemi bought a 904 out of a mid-80s Concord wagon to use in a drag race MJ he's building, and found that it does have a lockup converter.

I don't know what controls torque converter lockup on these trannies, but is it possible that the converter on your son's YJ for reason is not unlocking?

We will see, I'm a bit miffed that he has not called and given me an update on the status. I did not get a 4th cell phone for him to leave on his dresser I want to get under there and trace some lines and see if vac is involved anywhere.
Geeze, I hope it's not a tranny problem.