2002 Sonata stalls after start

[ed030690]

We recently got a new used engine for our 2002 sonata and alot of the parts on the engine had to be replaced. After that the engine was put back in and started up. It starts but if you dont hold the gas to keep up the RPM's it stalls out.(car is in Park). I was wondering if you guys know what could be the problem. maybe its a sensor or the computer i dot know. Please let me know. Thank you