JBR:

Your car has the simplest vacuum set up of all. Unfortunately the vacuum schematics are broken up and scattered all over the service manual with various systems. The two units on the firewall are for the heater controls. The levers on the console operate micro switches which activate the vacuum solenoids to either open the heater valve or close it. The default position for the valve is open for heat.

The solenoid on the passenger side is dirt simple to set up. The line to the manifold supplies vacuum to the solenoid. The other line to the distributor gets the vacuum to the distributor when needed. The electronics detemine when this all happens. At temps above 100C there is no vacuum to the distributor. At temps below 100C there is vacuum to the distributor. When the AC is on there is no vacuum to the distributor. And, at all speeds above idle there is no vacuum to the distibutor. When there is vacuum to the distributor it retards about 12 degrees. When the vacuum is off it advances for cooler running and better fuel economy.

From the above you can see the system components that affect distributor vacuum: the temperature switch, the throttle position switch, and the AC switch. When these are working properly the system is operating as MB intended.

That said, the simplest way to improve your car's performance is to try to set the timing to mimic european versions. And, the simplest way to do this is to time it, without the vacuum line connected, to about 32-34 degrees BTDC at 3,000 rpm. After making this setting you can re-connect the vacuum line and let the retard systems do their jobs. They only operate at certain times and even then they are not adverse to your performance. The US versions limit distributor advance to about 18-20 degrees total; when the vacuum is off to the distributor this is all you can get from your US version distributor. European models have more advance built in so with the initial lead there is about 32-34 degrees at 3,000 rpm, hence my suggestion to use this as your baseline. Fine tune it a bit for your gasoline.

For what its worth...

230/8

p.s: you need to invest in the MB CD ROM service manual. It is only $20 from MBNA. It is available here by mailorder: http://www.classictechlit.mbusa.com/MB/