1990 Olds. Cutlass Supreme

I have been having issues with this cr for a while, I have so far replaced the tps, map sensor, coil pack and module board, computer, and all injectors. About five months after getting it out of the shop with all new injectors we are having issues with the fuel again. It is over injecting, the fuel is filling up in the air filter and hose, and I can't find anything about this kind of problem in either the chiltons or Haynes manuals. I would like to get it fixed again, but I don't know what to do if someone could give me at least a clue as to wha tit could be doing that would be great.