My 86 240 started to run rich on the way to work. I replaced the O2 sensor, no fix. I put the computer in limp mode by disconnecting the mass flow sensor. The engine is still running rich, it throttles up even with the mass flow connector removed which tells me that there is too much fuel for limp mode (based on past experience with bad mass flow meter). I can't find the correct metric fittings to hook up a fuel pressure guage but there is no fuel in the vacume line for the fuel pressure regulator and the return line from the regulator to the tank pumps out fuel like a fire hose. Is there a chance I got a bad O2 sensor? I can't seem to find the test point described in the haynes manual. I checked the plugs and all 4 are equally sooty, indicating rich mixture on all. The timing advances like it should (checked with timing light)and appears to be correct, although it is hard to tell with the uneven idle. There is a bypass valve that ports air from the intake to the back side of the throttle valve. This valve is open all the time. If I block airflow the engine dies. Is this normal?

I'm out of ideas. Can anyone help?