I have an '85 300CD. I posted in the diesel section too, but didn't get a response.

I tore a bunch of the vacuum system apart yesterday, and it was all messed up. I have no idea what the guy was thinking the last time it was put together. I did find a few connectors with slow leaks, I am waiting to get some new ones...hopefully today.

I also hooked the mightyvac up to the main vacuum line, and it was pretty steady at 16 in/hg with or without gas. once I started hooking things up to the main line, it started twitching when I gave it fuel. Sometimes it would drop when revving, sometimes not.