My trusty 190D 2.2 daily driver (1000 miles a week +/-, 250K total) failed me last Friday for the first time ever. Halfway out of my mile long driveway it withered and died (as in no fuel). Walked back to the ranch for the 300SD and went about my day. Saturday morning I changed both fuel filters (which I had just changed a month ago), cracked the injection lines loose at each injector, spun it over and it purred like a diesel. Drove into town (4 miles) and back with no problem. Sunday morning I started for the village and 3 miles down the road it began to die again. Nursed it back to within a mile of the house before it refused to turn another rpm. Still had the wrenches in the car so I once again loosened the lines at the injectors, spun it over and had instant results, ran like a swiss watch. Back at the shop I clamped the throttle at 1500 rpms and let it run - for over an hour it never skipped, misfired, or in any way indicated that it might have a problem However.....
I have never been stranded by the roadside, and hope never to be. The only way to keep my record clean is to, as much as is humanly possible, diagnose and/or predict potential failures and practice good preventive maintenance. This car definately had a problem and I wasn't about to have it recurr 100 miles from home.
Lift pump was my next guess as to malfunction; checked out fastlane, $150+. Thought I best have a look before breaking out the plastic. On the 2.2 the air filter housing and intake tubes pretty much hide the IP and related parts from view. I had never had occasion to remove this assembly until now. Removed assembly and with all in view, pulled fuel line from primer pump and hit starter; fuel, fuel everywhere. Just saved the $150, but where to look next? Fuel lines all had been replaced at some point (prior to my ownership) are not MB cloth covered, but appeared good, not brittle or cracked.
Started the engine and watched while it idled; nothing to see. As I was trying to think of a way to replicate the problem I began to play with the throttle linkage. At about 1400 rpm I noticed the fuel lines begin to glisten; at 1800 they began to "sweat"; when revved up to about 3 grand they were pissing fuel in a dozen places. Happened to have some fuel hose on hand, replaced all the lines and, just like magic, no more problem.
It must have been pulling air into those lines until system air locked and could get no more fuel to the IP; damndest thing I ever saw.
Drove it 115 miles yesterday and 583 miles today and it never skipped a beat.
Something to keep in mind when dealing with an occasionally fuel starved engine.

Jim