Since I bought it 2 mos ago, my 1990 190E 2.6 with 77k miles is low on power off the line. 0-60 is 15 sec vs expected 9 sec. It also starts hard and idles slow and rough for a couple minutes. After that, except for the low power, it runs very smooth--no stumbling or missing. Here is what I know:

System and lower chamber fuel pressures are in spec-5.3 bar system with lower chamber 0.4 bar less.
Accumulator is new--holds 40 psi system pressure for hours after shut down (meets spec). Old one was bad, and the new one helped cold starting a lot.
O2 sensor was bad and I replaced it. Old one would not go above 1V even when heated to cherry red. New one did not help performance though.
EHA coil resistance is in spec. Disconnecting it makes no difference.
Temp sensor is good. Resistance is correct. Disconnecting it makes no difference.
Plugs are new Bosch copper. Old NGK plugs were clean and looked like they were running lean. All plug wires look very good.
Compression is 180+/-5 psi on all cylinders

Big mystery is that the CIS-E runs in open loop at a constant 10% duty cycle (at pins 2 and 3 of diagnostic port), and O2 sensor voltage drops from initial 4.5V down to under 0.1 V after it warms up. This all says LEAN which makes low power and acceleration make sense. Gas mileage is good. There is no detonation/knock. I am considering adjusting the mixture screw, but not until after I can get it to run in closed loop with fluctuating duty cycle and O2 sensor voltage. I haven't checked ignition timing/dwell. Any ideas??