Car is a 1980 245DL B21F with 274k. Runs great when cold, runs well when warm but idle is inconsistent (sometimes smooth at 1100 RPM, somtimes lumpy at 950 RPM). Bad gas mileage (18 MPG, used to get 21 MPG for the same driving cycle). New O2 sensor, cap, rotor, plug wires. Checked and found the following:

O2 sensor reads 0.55 V when cold, 0.0 V when in closed loop (running lean).

Dwell is steady at 49 (a bit on the high side, checked with O2 sensor disconnected)

Frequency valve doesn't seem to be getting proper voltage (0.36 V) with the engine off/ignition on. Lambda relay is getting ~11 V but when I tried jumping the connector terminals with the relay out (engine off, ignition on per Haynes) the valve doesn't buzz. I'm pretty sure I heard the frequency valve buzzing when the engine was on.

I would've concluded it was a bad relay had the valve buzzed when I jumped the connector. I was told the "computer" "never" goes bad in K-Jet systems. I'm hoping it's not a wiring problem to the frequency valve (grounds seem tight/clean).

Any suggestions for what to check next or pointing out the obvious problem I'm missing? Thanks!

Zack
1980 245DL M46 274k
1988 745T+ M46 197k