A bad diaphram can cause oil to be sucked into the intake manifold, however, a bad diaphram is usually accompanied with other symptoms such as hard brades due to less vacuum to the brake booster and you will frequently notice rough running of the engine because of the excess oil getting to the cylinders. Check for a bad diaphram is easy: Disconnect the line from the vacuum pump to the intake manifold at the vacuum pump---look into the pump fitting and the end of the line you disconnected---if you see black engine oil, you have a bad diaphram. Regarding your oil comsumption, make sure you don't have any oil leaks. Two common locations for leaks are where the oil filter bolts to the engine block and the bottom of the oil cooler next to the radiator. The oil cooler core tends to rust at the bottom leaving you with small pin-holes.

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K. Weimer
300SD (1)
300D (5) [Plus 1 parts]
300SEL 4.5 (2)
280SE (4)
280 (2)
250 (1)
250SE (1)
240D (7) [Plus 1 parts]
220D (11) [Plus 3 parts]
200D (2) [Plus 1 parts]
180c (with sunroof)

1995 Nissan UD1800 rollback
"If I can't fix it, it don't get fixed"