2003 E249 Automatic. Starts fine but stalls when you put it into gear

One of the most common failures that can cause this problem that I have seen before is the Torque converter solenoid (TCC solenoid). This solenoid can stay stuck on and cause the torque converter to stay locked up, this will cause the vehicle to stall whenever it is put into gear. The vehicle will start and run fine in park or neutral but will stall out as soon as it is put into gear. This is the most common failure that can cause this.
Also a malfunctioning idle air control valve can cause this, if the valve isn't moving or responding to bump up the idle when put in gear it may cause the vehicle to stall out, the computer commands this valve to allow more air in to bump up the idle to compensate the load on theenginewhen put in gear, if it isn't moving or isnt moving fast enough the idle may be too low and could cause the engine to stall out.Have also seen bad crankshaft position sensor cause this ,as well as mass airflow sensor's ,TPS - throttle position sensor's . Your best bet , take it to a qualified repair an have it diagnosed . No guess work .

Does it happen when you shift just to 1st
what is idle in park
when you turn on the ac in park does the idle go up a hair??

Check for broken breather hose from valve cover and follow it under the intake. You may also have a ruptured diaphragm crankcase ventilation valve (vac leak), bolted under intake manifold.

might just need a good tune

Have u checked spark plugs.?

Engine stalls or RPM fluctuates at idle up and down or dies near idle.

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve but always run a OBD2 fault code as well as the cleaning procedure. Buy a can of throttle valve cleaner (do not use carburetor spray cleaner!) from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control

If it starts back up and does not stall when you put it in gear it is probably is a problem with the torque converter lock up solenoid, on some vehicles you can disconnect the connector on the side of the transmission to the lock-up solenoid and the transmission will work fine without lockup if you do not want to replace the solenoid.

The TCC solenoid in the transmission needs to be replaced. It is under the side cover. It controls the converter to lock up for better fuel mileage. If you want to drive car until you get it fixed you can un-plug the connector going to the transmission on the front of transmission. This will keep it from going to lock up mode and keep it from stalling until you can fix it. Common problem.

if it is an automatic the torque convertor could be locked up.

you need to adjust the engion timing