1995 Buick Riviera wont stay running Buick Riviera 95 start

Engine Mechanical problem
1995 Buick Riviera 6 cyl Two Wheel Drive Automatic

Okey here we go I have got this car buick 1995 riviera car wil start just fine. But wont stay running. I can get the car to stay runnig if I pump the gas and work at it. It will rive up [let off dies].I know check the gas pressue its [50] on gauge I dont think its the gas here. Why I say this. I just bought this thing for a good price or I hope?I guy said he had to change the key/lock in cloumn and he dont have the key flashed or car. He said thats when it started to do this. And it run just fine before the key/lock broke he put in new motor pick ups [timeing] I called a lock smith and they say thats what I need' [flashed] but I called some one that works on car's they said the car wouldnt start at all ? The reason I got this was for the motor. I have a 96 buick thats the same car [no tubo] I wanted to put the motor/ train's in it. But this thing is in better shape then my 96 if I can fix this and use the other for parts OBOY Iam to the piont were iam going to take it to someone [FIX IT]