1999 Jeep Grand Cherokee Limited 8 Cyl 4.70L
I get a check engine light with code P0108, high manifold pressure, what causes the high manifold pressure?
The engine will hesitate just prior to the light coming on. It usually happens around 1600 RPM and the pressure read is 15.1 psi. The engine has new spark plug coils and throttle position sensor.
You have a very high probability that the map sensor is the cause. replace the map sensor. There is a much smaller chance of the upstream oxygen sensor signal wire being shorted to ground. (that could cause it also) but it is not common. I would just go ahead and change the map sensor. It is a real good bet.