I'd really love to know where you get your information...

The rev-counter and idle-control on this generation of diesel is controlled by the EDS system. If the EDS is not working, or not receiving a pulse count from the flywheel pickup, you won't have tach or idle speed control. The car will still run, but idle will be very low. There's no communication from the tach involved. Tach operation is passive in these cars. Pulse train sent out from EDS, tach converts it to a speed. That's pretty well it.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

Ok, one part fixed. The car is charging correctly again, 14.45 volts. Still no tach or idle control. I mean, I can live without it, and just manually set the idle up on the IP. I got the new tester for reading the blink codes. Socket2 gave a single blink, which if I'm reading it right means it has no errors. Socket 2 is the one that would show the EDS.

I did notice that the speed sensor wire is pinched between the trans dip stick and engine. I'll have to free it and see if it's shorted or broken there.

engine sounds great now. the knocking is gone, the new belt tensioner shock and pulley seems to have made a world of difference.