Ever since I got my modern glass Mooney 2 years ago, I've had erratic problems with my manifold pressure indicator on the MFD. Several avionics guys have got it working again(a different diagnosis every time), but after a while I start getting erroneous readings again.
It reads a pressure lower than actual, erratic, up and down. The problem has always been a connection somewhere. Usually the large wire harness that goes through the firewall. Take em apart, clean em then back together again and it works fine for a few hours.
There is not a lot of Mooney G1000 avionics repair experience in my area.
Obviously, it's a loose connection, but cannot nail it down.