The TB vacuum is ported vacuum.

The idea being to suck in fumes from the purge canister only when under load.

Take a look at the diagram below and tell me if i got the right one?

You now, too much vacuum to the distributor would yield to much advance, which would cause hot running.

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Thats no my vacuum setup. Close, but not identical. There is no vacuum line to the distributor on my car, it goes to an advance module/coil. And some other lines do not match. This is the diagram I used.

Attached Thumbnails

 

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

LYL:

In checking the condition of various vacuum lines you noted that removing and reconnecting the line to the ignition unit (EZL) caused a change in engine speed; that's a good sign; at least that portion of the EZL is working.

A couple of additional checks are in order. Do you have a timing light, and an ohmmeter?

With the timing light, check the timing at idle speed, and up to about 3500 RPM. With vacuum, idle: 10-14 BTDC, 3500: 40-44 BTDC. Without vacuum, idle: 3-7, 3500: 24-28.

With the ohmmeter, check for continuity from the temp. sensor to the temp. terminal in the plug on the EZL. Which plug on the EXL do you want? If you were viewing the EZL such that the two plug connections were "down", and the vacuum connection were "up", the plug on the lower left contains the temp connection. It also contains the throttle valve switch connection, and the reference resistor connection, and an unused connection. On the dual temp. sensor the two circuits are connected diagonally, one supplying the temp gauge, and the other the EZL and the ECU. If you pull the insulation jacket back a bit (at the sensor) the green with black tracer is the wire you want.
What's all this about? If there is an open circuit between the sensor and the EZL, the advance range of the EZL will be partially inhibited, resulting in less advance than is required for proper warm-engine, cruise operation. This inhibition of advance with a cold engine (high resistance) is a design feature to speed the heating of a cold engine!!! Seems rather consistent with what you are observing. If the EZL never gets a warm signal (low resistance), the advance remains inhibited, and the engine runs too hot.

Just a thought, but do you have a temp gun? The kind with a laser dot that gives you the surface temp of what you are pointing it at. Also you can unplug the coolant temp sensors and check the ohm readings. This will get you past the potential ground issue.