Overfueling like crazy

[Divine02]

95 Camaro Z28. 383 that has had the ECM tuned on a dyno. Car was having problems before we freshened up the motor. Just got the motor back in it and it did start but it's flooding out. The plugs are soaked in fuel. I've never seen a motor over fuel this bad before. Finally got a Snap On Scanner hooked up tonight and the only thing I have seen that is wierd is the desired idle. It is at 3180 rpm. We hooked up a factory ECM back to the car and it is still reading the same thing. What tells the computer that the desired idle should be up so high? I also thought the MAP sensor was bad cause it was reading 4.5 volts but apparently it works backwards from what I thought. Hooked up a known good MAP and it still reads the same thing. All of the test and voltage readings were taken with the key on engine off because the car will not start. It's shooting fuel out of the exhaust and has been backfiring like crazy. Any suggestions?