My 1991 Loyale Wagon with auto tranny and 225,000 miles has been running well. However, weather here in Portland, OR has gotten a bit cold, high 20s-low 30's. It will start fine but the engine dies after only 5-10 minutes.

 

Any ideas why?

Likely having trouble getting air or fuel.  You'll need to check for:

 

-- any computer codes

-- air filter problems

-- fuel filter problems

Fuel pump relay?  They get flaky with age.  They can work fine when cold, then open up when they get warm.   So the car starts fine, then stops running when the car  is warmed up with the heat on full blast.

 

When it happens, plug the green connectors under the hood together, and listen for the fuel pump to run.  It will cycle on and off with the connectors together and the ignition on, but the engine not running.