Hi all. Here's my frustrating problem:
My car is a 1990 300CE with 110k miles. The car runs like a champ with no hesitation at any speed, idles good, starts great, etc. BUT the lambda is at exactly 81.36 according to my Sears multimeter, and this is with the key on, engine off AND at idle. It doesn't change.
My service manual says:

"Key on, engine off-80%= Transmission engaged in gear."

"At idle-80%= Data exchange between ignition control module (N1/3) and CFI control module defective."

If i turn the idle mix screw the lambda doesn't change, the car just runs worse.
I've cleaned just about every connection that I can here with no change.

I failed the smog at idle (HC was 329, max allowed is 120), but passed at 2500 RPM (HC was 46, max allowed is 140.)
I've cleaned just about every connection that I can here with no change.

Any ideas would be appreciated.
Thanks in advance.