I have a 1990 240 DL, w/ manual x-mission and LH 3.1, 203K miles.

I'm getting the 2-2-1 and 2-3-1 error messages on system 2. (Fuel System compensating for extremely rich or extremely lean air/fuel mixture at cruise)

Car idles higher than normal and is pinging under load.

Fuel pumps seem to be operating O.K. I hear both of them working. I haven't checked the fuel pressure regulator. It it worth considering?

Another funny symptom - the hose connecting to the accumulator for the environmental control pneumatics is making noise when I accelerate. I think the check valve there is sticky. I disconnected the hose and plugged it up, but the car is still running lean.

Loosening the oil fill cap causes the cap to rattle - indicating some crankcase pressure. But flametrap is clear.

I've checked for vacuum leaks in the flame trap line above the oil sep. canister, the hose going from the manifold to the PCV, the idle control valve hoses, the big tube down stream of the Air mass meter and all both of the hoses connecting to it. I've also sprayed carb cleaner around the intake manifold to look for leaks (hoping for an increase in engine RPM).

I am suspecting a vacuum leak somewhere but am hard pressed to find it.

Could it be the oxygen sensor? I did the Bentley check of the O2, and the voltage is out of spec. It moves from 0.15 volts to 0.95 or so at idle when the engine is hot. Bently suggests 0.4 to 1.0 volts. But couldn't this also be due to a vacuum leak?

Timing is O.K.

Any suggestions?