Erratic Manifold Pressure 912ULS

Not familiar with the Dynon D-180 however if its anything like a regular mechanical gauge set up, there will be a small tube from a T fitting on the inlet manifold cross over tube. If the tube has fatigues/perished/been damaged it will suck air and give a false reading. Movement of the engine, prop pulses through the cowling may cause a small split to open/close momentarily causing your erratic readings.

If the tube does not have a small idle jet orifice in it to reduce any erratic pulsation then put one in.

A purchased an automotive VDO manifold pressure gauge, about 3 years a go. Connected it to the OM T fitting on the carburettor balance tube. Worked straight out of the box. Came fitted with a restrictor in the "inlet" fitting of the gauge.

That’s what I have I think…may need replacing. 

Another pic