Engine is stalling out while driving

It sounds like he left something loose. Have you checked all connections? Also, check for body grounds that may have been left off.

Let me know what you find.

Joe

Have you checked fuel pump pressure? Has the check engine light come on?

Let me know.
Joe

I am sorry you are having trouble.
After all, a 14 year old van with 140,000 miles should not have such failures.
The stalling may indeed have something to do with this. It depends. When was the last trans service? I think it is supposed to be done at about 3 years or 36,000 miles. It should not have failed, or if it had a problem, you think you may have seen something then.
Also the throttle body, it is a recommended service at about the same time to remove the dirt from the sensors and give it a clean idle, also a fuel injection service would clean the system and injectors also. But even though I am sure you have serviced it well, or hopefully the owner before you did, these failures have occured anyway, if you like the van, it may be worth repairing but have the mechanic make sure it is worth putting a couple of thousand dollars into a transmission overhaul. The engine or some other expensive part like the fuel pump may also need replacement soon.
Good luck. It is rare for the transmission to cause it to stall. But it can happen.

Low fuel pressure have it checked

If it is the one the back close to the passenger side, then yes. It is your #1 spark plug. The PCM uses #1 spark plug for timing, fuel delivery and a whole lot of other stuff. If that plug is bad, the whole motor won't run smoothly.

Also, you have OBD-II compliant PCM. Take it doen to Autozone or Checker O'Reilly and have them scan the computer. COme back with the fault code(s).

Have you checked the wiring harness to the PCM to make sure it is clean and tight?

Of the items you listed, the only things that would cause a stall is the map sensor or throttle position sensor. As far as the gas cap, if it leaks fumes, that won't have an affect on the engine.

I have to be honest. Neither would shut down communication to the PCM. As far as the stall, both can do it. The TPS is more likely to cause a problem when you touch the throttle. At an idle, the vehicle should go into a default mode and continue running. As far as the MAP, it could shut the engine at any throttle position.