2000 Mercury Mystique

Does it start back up easily when it stalls if not might want to do below to try and catch it what's causing it. Corrosion/bad ground etc

Get a helper disconnect a sparkplug wire or 2 and ground it to the engine at least 3/16 away from ground -have helper crank engine over-do you have a snapping blue spark? If so-you have a fuel related problem, Do you hear the fuel pump come On when you turn key on? If not check fuel pump fuse and fuel pump relay if so, check the fuel pressure to rule out the fuel filter/fuel pump/pressure regulator and listen to the injector/s are they pulsing or hook up a noid light. No snapping blue spark continue to troubleshoot the ignition system-power input to the coil/coil packs, coil's resistances, distributor pick-up coil, ignition control module, cam and crank sensors and computer Note: If it doesn't apply disregard it.

That will be ignition / spark plug-related or the weather seal is deteriorated or missing on an electrical connector. When the engine is running and still cold, use a spray bottle to spray water on the electrical components. If you see arcing or sparks jumping, typically from an ignition coil, that needs to be addressed. Also spray connectors and sensors. If nothing causes the engine to stall, you may have to crawl underneath to check the wiring to the fuel pump.