Check behind the instrument cluster. These are the leaks I usally find:
1 Door Locks
2 A/C elements behind dash and glove compartment.

BAD NEWS IS A DIESEL DOES NOT HAVE VACUUM!! Only pressure. Thats why they have the vacuum pump on the front of the motor. If it is running rough at idle try opening the lines at the injectors one by one. My bet is that you will find either one injector that is not injecting properly or at all or you may have a dead cylinder with no compression. Its just like testing for a dead cylinder on a gas car except there are no spark plugs so you will have to deleat fuel from one cylinder at a time to see if it makes the car run any diffrent. The one that you open that doesn't make a change will be the dead cylinder.

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DRIVE HARD-DRIVE FAST-DRIVE TO GET THE HELL OUT OF MY WAY.

1986 190E 2.3-16 Pearl Black!!
1987 190E 2.3-16 Smoke Silver!!
1986 190E 2.5-16 Pearl Black!!
2004 CLK 500 Cabrio Designo package!!
1994 E320 Cabrio Red with black top!!
1985 500 SEL Anthracite Grey !!
2011 Subaru Impreza STI 380HP (Yeah Baby)