Long story short – 2018 Outback 3.6 R with 70,000 miles. Went to town with new spark plugs, front and rear diff fluid, and new brake pads all around (fronts had about 10,000 miles left, but the rears were done).
I now have a firm brake pedal with the engine off, but it sinks when the engine is running. The only thing out of the ordinary was… the fluid was flushed about 10,000 miles ago, so it was higher in the Master Cylinder than I predicted, and I pushed fluid out of the cap with the first caliper squeeze like an amateur. 
I’ve:
- Cycled the parking brake multiple times.
- Bled the brakes thoroughly (40+ oz of new Dot 3) using a vacuum bleed with teflon tape on the bleeder screws – in the order listed in the FSM (RF, LF, LR, RR). No bubbles.
- Tested the brake booster check valve.
- Checked the booster by way of FSM test procedures – without gauges.
- Have a high and hard pedal engine running, with no vacuum going to booster.
So before I go buy a bi-directional scan tool – or throw in the towel and take it to the dealer….
Any thoughts on it needing a good ABS bleed? Or, does it sound mechanical like a bad booster?
All thoughts welcome!
