Chasing vacuum behind firewall / Rough idle 123

[Panzer_Man]

I have an 83 300D turbo diesel 230,000m in Florida.

For years it has intermittenly (months) CLUNKED on downshift, failed to turn off for 12 seconds in cold weather etc... My mechanic was clueless and I finally figured out it was the vacuum. So I fixed the hoses and everything was sweet.

Next half of story:

Since I've owned the car it has idled roughly only when the engine is well warmed up , AC on and in gear. The whole front end shakes. I've finally had enough and in the last 3 months had:

-motor mounts, dampers and engine shocks replaced
-valves adjusted
-injectors replaced
-engine damper screw replaced and adjusted

$800 later the bastard still shakes. To add insult to injury, the first thing listed was just done by my mechanic and now the vacuum problem has come up again.

Qs:

1. What have I/my mechanic missed that may be causing the rough idle problem?

2. All my vacuum hoses check out under the hood but something must have come loose. Can I look around where the hoses enter the firewall? Is there another way to track down a vacuum leak?

Many, many thanks in advance,
Matt

[BENZ TEK]

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.