Anyone Know about Lambda Control?

[ctaylor738]

I know that this is off-topic for this forum, but nobody on the tech board answered, and I know you guys will help if you can.

The Wayward Woman ('81 380SL) is running well with the exception of two problems that I think are related.

1. Running very rich at idle, but OK at other RPM
2. Surging idle in Park: bounces between 480-580 RPM

I ran the basic checks in the manual on the idle control, and that system seems to be working. My theory is that the lambda system is not working in closed-loop and sending bogus signals to the idle system.

By bridging the temp sensor, which simulates cold running, the idle went to a rock-steady 750 and vacuum stabilized at 16 inches.

I was able to verify that the lambda control is getting 12V, so the OVP is OK.

When I put a dwell meter on pin 3 in the diagnostic socket as it says in the manual, I got a steady reading of of 6 degrees, which is like 6% (very rich) when it should be fluctuating between 42-50 degrees.

So there are three components involved. The O2 sensor, the lambda controller, and the frequency valve. The sensor is a no-brainer at about $20. But the frequency valve is expensive and the controller is a budget-buster.

Does anyone know a bench-test for the frequency valve so I can tell if that's the culprit, assuming the O2 sensor doesn't do it? Other ideas or suggestions?

Many TIA