86 2.5l Cutlass Ciera Cutting out--Please help

Hey everyone...first Id like to say hello to everyone on the forum. I need help on my latest car problem.
I have a 2.5L 86 Ciera that is cutting out on me. THe reson its dieing is casue the Throttle body injector is not firing. If the engine has been sitting for a while the TBI will spray and start right up. But it'll run with an erratic idle and will increase and decrease RPMs repetedly. Then a few min later the TBI will shut down and kill the engine. The injector is good itself.
My guess is the ECU is telling the injector not to open. Im suspecting the ECU. I just changed out the TPS and the fuel pressure is good. If its not the ECU, what sensor tells the computer the rpms of the engine? Im also guessing that the ECU thinks the engine has 0 rpms and then shuts down the fuel. If it sits for another 30 min, you can start it up again and it'll do it all over.
Please let me know what you think. I cant figure this one out. Thank you. ERIC

Anyone??? Please help me out

My first sugestion is get a different car. Most cars made in the 80's are junk. Second, get a book for your vehical and find out how to get the trouble codes. If you have no trouble codes then your trouble is mechanical. I dont know how old your fuel pump is but I check it out. even though your are getting good fuel pressure your fuel pump could be getting hot and cutting out. You also need to see if your fuel system sustains pressure. If it cannot sustain pressure when the vehical is not running then you have a bad regulator or fuel pump. I do not believe you have a high pressure system but if you do GM uses what is called a fuel pulsation dapener. If it is bad or missing it will give you similar symptoms. As I said though, get a book and get trouble codes. Hayes is a good book for the shade tree Mech.