Engine won't start after replacing inlet manifold. It backfires thru throttle body. I changed plugs and wires one coil and one injector. Also found intake was partially blocked with rubbish so sprayed heavy with MAF cleaner also removed and sprayed idle sensor with cleaner any suggestions. The year is 1994 Cutlass Ceria wagon V6 3100 fuel injection.
You need to go back to basics. Check for spark at the spark plugs, if no spark is there then check the primary components of the ignition system like the crank sensor, cam sensor, ignition coils and all the wiring going to components including the proper wiring and firing order of the spark plug wires.
Check for fuel pressure. If no fuel pressure, check the fuse for the fuel pump and fuel injection system, fuel pump relay, fuel pump, and fuel filter. When you turn the key on you should hear the fuel pump go on for two seconds and then turn off.
Try these suggestions and get back to me with your results. We can continue doing diagnostics from there.