my supra goes dead

hey i have a 93 supra na auto i purchased it from a guy in town he didnt take care of the engine it was nasty oily and greasy i put degreaser on it and washed it off well i waterlogged it i cracked the disturibter i replaced it still wouldnt turn over it would pudder but wouldnt turn over so i took the intak off so i could get to all 6 plugs the chambers were covered with water i get all the water out with a shopvac and take the plugs out and clean them all and fix everything back it will run now as long as your driving. when you crank it up the RPM is at 2 and its chillin ideling good then as the engine warms up it graducally loses RPMs and it gets down to 500 it feels the engine is strugging to stay running it jump 500-1000 RPMs then it goes dead but driving is fine it drives perfect please help me someone i am hurt i had my baby for a month and i payed 11k for it