Q: stalling engine

starts and runs fine from a cold start but after it gets warmed up it will completely stall on my when i let the rpms drop to low or i come to a stop, it will also studder while im driving down the freeway at 70mph, i dont let off on the gas or anything and it will randomly lose all acceleration, coast for a lil bit and try to spudder back to life, kinda backfire before it gets going again or it will just coast til it dies completely, it will start right back up and i can even throw it in nuetral and restart the engine while coasting. i was having huge problems on a long trip and i found that if i feathered the throttle back and forth just enought o maintain my speed then the studder stopped, but just as soon as i try to maintain a constant throttle position again it will try to studder and die again

My car has 222000 miles.
My car has an automatic transmission.