So i've been running ethanol e85 in the car for the last 6 month with bosch "400" injectors rated at 46 lb/hr.
Recently withing few thousand miles this have been changed: plugs (bosch coppers)/fuel filter/ignition wires/distributor cap + rotor/intake manifold gasket/vavle cover gasket with some red rtv in the corners/front seals 2 cams + 1 crank/ oil is current apparently. Cleaned AIV and throttle body with cleaners/did seafoam 2 times in last 6 months.

I have to admit that i'm due for vacuum lines overhaul.

car has 129.8K miles. it's 944T with auto transmission. Transmission fluid has been flushed through the trans cooler lines at radiator.

Symptoms are as following. After i start the car cold or hot. I could feel it surges once every 10 seconds or so. It feels as if some wave goes through car's body. Also tachometer bounces +/- 100 rpms. Somtimes the tach would go to the first line after 0 rpms (?what is that number?) and would stay ther, other times it's in the middle between that one and 1000 rpms.
I have a calibrated vaccuum/boost gauge and it also moves +/- 2 inches of Hg (correct units i assume) when the surge happens. It usually stays in the range of 10 to 12 inches of hg at idle.

I'm at 5000 ft above sea level.

Compression test resulted in this numbers 120 120 120 135 (without oil i think)

Could you guys steer me in the right direction. Also i think my fuel economy could be better.

Could a valve cover gasket cause vacuum leaks?