Check compression when the engine is cold, then when it is at operating temperature. Best bet is to have codes and history codes read. Unplugging the MAP throws the computer into default mode. This could be the MAP sensor. But on Fords, it could be bad vacuum lines also. A scanner tells me this. Check compression when the engine is cold, then when it is at operating temperature. Best bet is to have codes and history codes read. Unplugging the MAP throws the computer into default mode. This could be the MAP sensor. But on Fords, it could be bad vacuum lines also. A scanner tells me this.