Volvo Repair: 1987 Volvo 240DL Wagon - (automatic), coolant temperature sensor, coolant temp

Question
my car runs well when cool, but stalls out during idle when it is warmed up on a hot day. It starts right up again and I can keep it running by putting it in neutral and reving the engine. I have noticed that the temperature gauge starts out normal but after the engine is really warmed up and the stalling begins, the temperature gauge goes down to cold. I've had the airbox thermostat valve  replaced and the throttle cleaned. Could it be the coolant temperature sensor? or air mass meter?

Answer
Esther, that airbox tsat is useless.  More than likely your theories are correct.  I would test the meter by unplugging it and let the car surge.  Now plug the meter back in.  If it stalls then the meter is bad.  The coolant temp sensor is more for starting issues but it can also contribute to the stalls.  I would also clean and adjust the throtle body.  Roger