Steve is right relative to the dwell meter than a digital volt meter. I suggested the dwell meter for I thought more owners would have one than the digital. The Factory Service Manual Engine 103 section 07.3 states "IF NO LAMBDA CONTROL TESTER IS AVAILABLE, A DWELL ANGLE TESTER MAY BE USED". The manual lists the procedure as well. The best I've seen was with a Fluke 98 Scope Meter mdlII.

The specifactions per M/B are,
idling speed: rpm 650 +/- 50
control range: 35-45% this is of peak battery voltage.
dwell angle 21-27 degrees
I don't mean to be oposite with Steve, this process was taught to me my my M/B dealer's Technican. And if I may this is my technique and it has worked excellently for 12 years.
You can obtain the Allen wrench from your M/B part Dept.
I believe it is 3mm.x 6" long with a "T" handle.
Hood open and Vertical.
You will need a Dremmel Tool and a carbarundium cut-off disk.
After removing the air filter and covering the air intake; using the cut-off tool, cutoff 10mm from the Lambda Tower, NO MORE than 10MM. This removes the safety ball. You can cover the hole when your finished. If you are a purest you can purchase a Lambda kit when you buy your Allen wrench.
Insert your "A" wrench and push to feel the spring of the adjustment screw, it's very sensitive a little move makes a terrific change. Be careful, don't turn it yet.
Locate the round diagnostic connector on the left inner fender panel. Connect the positive test lead of your dwell meter or what ever you have(DVM or SCOPE)to pin #3 and the negative lead to a GOOD chassis ground.
Set your test device to the proper range.(dwell mtr 20-30- degress, scope to 30-50%, DVM dcauto).
Check for2.5-5.0 vdc or 21-27 degrees dwell, scope 35-45%.
Disconnect and plug the purge valve at the throttle valve assembly.
Install the air cleaner.
Start and run the engine until it reaches operating temperature.
Snap the throttle then run the engine at 2500 rpm to warm the o2 sensor.
Check your meter readings.
Return engine speed to idle.
If the readings are off, inseert your "A" wrench through hole in air filter. Feel for the adjusting screw.
Make your adjustment, very slightly. Remember you are making a fuel discharge adjustment. Wait for the O2 sensor to respond. You want middle of the spec range.
Vehicles and climate vary, tweaking may be required for that smoooth idle, but stay in spec.
Apply emergency brake and put Transmission in Drive.
Idle should be smooth and speed right. If not smooth enough repeat your tweaking.
Your DVM on pin #3 should read the average voltage, approx. 50% of peak voltage and the dwell meter approx. 50% of range.
Unplug the O2 sensor under the passenger carpeting. KEY OFF, ground the lead to the control unit. Connect your meter to the single wire from the O2 sensor, now start the engine. A reading of 0.45- 1.0v(full rich) means the sensor is responding properly.
Remove and replace the air filter, unplug your meter and return the cover cap.
I use a tubing cap to seal the lambda tower.
I hope I havent left anything out, possibly Steve can help us both.

Donald
odd ball out