What are the possible causes of my 190E 2.3 running rich? What tests can be performed to diagnose?

The testing is described in the DIY section under evaluating engine controls. Complete testing will also include fuel pressure testing.

Thanks for the info, Steve. I can't find the DIY section. That's probably a bad sign! How do I locate that?

Thanks for your help.

Darrell

Look at the top of the page! You can't miss it! DIY.

Help interpreting data
 

I went to the DIY section and consulted my PM CD reagrding testing air/fuel mixture with a multimeter. I got results that aren't what I expected.

With the O2 sensor disconnected, it started out at 6.5V and the temp indicator on the instrument panel indicated typical operating temperature. After idling for several minutes, I noticed that the ranges were increasing so I unplugged the sensor again and the voltage had risen to 6.92V. The PM cd says it should measure 2.1-4.8V.

With the sensor connected, the voltage did oscillate. The range was +1.3V to +1.7V from the 6.92V baseline with the sensor disconnected.

I also noticed when I removed the air filter lid that the "choke plate" (?) was closed when the car was not running. Is that normal? On all my domestic vehicles, I believe the resting position was open.

What fun! Thanks again for all your help.

Darrell