W201 KE Jetronic strange problem

[akorna]

Good Morning,
I thought I'd toss to the forum for advice - been chasing a poor/no start/poor running condition for some time on my 1991 190e 2.6 that previously ran beautifully - 98K miles on the car.

I've attempted most electrical/fuel troubleshooting, but if the car starts, and I monitor duty cycle, after warm up the cycle drives to "0.0," after going into closed loop. If I disconnect the EHA, it goes to 90+ and stays there. Adjusting the mixture screw with the 3mm allen wrench does not appear to have any impact.

Vacuum is at best 16" Hg, and can be as little as 10", but I can't seem to locate a vacuum leak.

Compression is 180-190 on all six cylinders (cold). Fuel Pressure is 79 psi at the top of the FD, 72 at the bottom. I had rebuilt the FD back when this was just an intermittent problem.

Temp sensor is relatively new, and checks within spec at the EZL and the sensor. Getting spark to plugs.

Oxygen sensor voltage is 0.85v when EHA connected and .27v disconnected, which seems to match rich/lean conditions.

I'm thinking there is a mechanical issue with the air-flow sensor, lever arm, mixture adjustment - so I'm prepared to remove the entire assembly to check. Any other ideas?