The ‘tested’ replacement MAS unit did not solve the issue. So I decided to dig a little deeper.
First, some important additional background info. About 4 months ago the car started to cut out - once every few days - for no apparent reason. About 3 months ago I found a length of wire in the harness behind the battery that had melted insulation. The wire color was white with red stripe. None of the surrounding wires were damaged.
So I replaced the damaged wire from the MAS unit plug..
.. to near where it goes around the back of the engine - under the vent box. This appeared to stop the intermittent cut-outs.
Note; the above picture shows how the area where I joined the new-to-original wires looks now. But it was fine when I did the repair.
This evening it became abundantly clear the rest of the original wire – which goes across to the drivers side front fender - is bad. It got hot at some point in the past and melted the insulation.
I would like to obtain a good harness if anyone has one available. Car is a 1991 190e 2.6.
Alternatively, I will have to rebuild the old harness.