This depends on alot of things my suv would idle fine in park while ac or heater was on but would stall in gear and would run fine in park or in gear if ac or heater was off the problem lied in the throttle body of my vehicle small particles had built up around the (butterfly) and was not slowing enough air to pass while at idle in park with ac or heater on I pulled the breather hose off opened the butterfly with my finger (caution these parts have sharp edges) and cleaned with gumout carburetor spray ( note engine was turned off) and u should replace your air filter while your at it ( assuming your vehicle is fuel injected)
Ignition module is bad I had a similar problem on a Pontiac grand am- it was the torque inverter. It would idle fine, run in nuetral, but as soon as it was put into gear it stalled with a thump.
Hey tom its a 1990 pontiact transport van and it starts out fine and as soon as the vehicle warms up it will stall it will start back up but when you put it in gear from park it stall again until cool?
The vehicle would stall when put in gear would be the fuel pump. The fuel pump is very weak which would explain why in neutral the vehicle starts if it gear it would have to have more gas.
vacuum leak,map sensor
Symptoms of a bad converter vary. The vehicle may not move at all when in gear. The vehicle may exhibit engine stall when put into gear or may not have power during takeoff. Also shudder may occur when under load. Noise in the transmission when put into gear forward or reverse.
A problem in the fuel line could cause it to stall. On a stick shift, letting off the clutch too soon would cause the vehicle to stall.
TCC Solenoid.
ck motor mounts.when bad front mount will loosen ground cable,its on the mount
Look for a vacuum leak.
if you got an automatic depending on what gear it is you may need a 2800 or 3500 rpm stall in your torque converter call a transmission shop if that's it they will help you
You need a tune-up
It depends on the gearing of the car. If you are in the highest gear and 40mph in that gear is under the idle rpm of that car than you will stall.