1998 Plymouth Voyager 3.3L - Stalls at start and during deceleration

If it was a two cycle I'd say it was clogged exhaust ports. But you have a pretty exotic bike. So I guess it's a timing issue dealing with the exhaust Ox sensors.

Change the coolant sensor but make sure the coolant is full up in the radiator. When this sensor malfunctions, it sends the incorrect signal to the computor & it stays in the incorrect timing mode & the car stalls. The sensor is close to the thermostat housing. Good luck. When the engine is hot, unplug the sensor & it will start immediately. Again, good luck!

if thi plymouth voyager as a 3.3l eng it does not have a timing belt it as a timing chain does not require any maintenace as all like the good ol days ..if it as a 3.0l eng then it as a rubber timing belt that control the valve timing that reqires replacing every 80 to 100, 000 miles make sure you know what engine this van as if its a 3,3l it wi say it on top of intake or 3.5l is the same they both have chain ...3.0l does have a timing BELT

This may be caused by the idle air control sticking.
BTW, warming up a modern vehicle for the sake of the engine is not good; driving it off gently will bring it up to operating temperature more quickly and reduce wasted fuel. The engine just shouldn't be operated at high revs right away.

What are the trouble codes? Can be a lot of things, but still sounds like an ignition problem (bad coil pack?).

the most likely cause of this problem is a defective fuel pump, the reason it starts and dies is there is some presurized fuel still in the lines, that lets the engine start, but since the pump isn't working it runs out of pressure and stalls, the fuel pump is located inside the fuel tank, this is a job best left to a professional shop.

try changing the fuel filter first, that is usually the simplest fix and the most overlooked filter on a vehicle...

do you have a service engine light?
if so change catalyst. and both o2 sensors.

exhaust. replace converter.

most of times stalling problems are related with crankshaft sensors have your crank sensor replace and see if this will take care of your problem