My 7.3 runs great when the service engine soon light is on. When the light turns off, why does it run rough and sometimes stalls?

Throttle position sensor or maf sensor malfunction.

Best get codes first no guessing.

repost with codes and you will recieve the help you want... the systems monitered by the light are all directly related to a running engine. turning over slowly could be battery or starter (cold weather does affect battery charges).

Service Engine Soon came back on and the car is again stalling ????? Did you have it checked for DTC'S - diagnostic trouble code's ? Service engine soon light on , codes will be present !

Check TPS sensor[RPM]and IAC sensor.

a defective oxygen sensor will make vehicles run rough and will stall out

I just had a similar situation. The truck would run fine and then the Service Engine Soon light would start blinking and the truck would go into "limp" mode. It would eventually stall. Strangley though, if I turned the key over and then restarted it, it would start right up and run again. It ended up being the IPDM (Intelligent Power Distribution Module) that was bad. It cost me $520 to replace it.

If it does not do it in park or neutral, it could be a number of things. One being a sticking Torque Converter Clutch solenoid (TCC). It could be that it needs a simple tune-up. How often does this problem happen?

Go to Advance or Auto Zone and have them run an obd scan on it and it will pin point why your light is on and could solve your problem. This is often done for free.

sounds like you have a vacuum leak, check all the vacuum hoses and replace any broken or kinked ones, also check around the intake manifold gasket for leaks. any air leaks after the air flow meter creates 'un-metered' air which inturn will make the car run rough and stall, hope this helps