This problem is driving me crazy - if you have any suggestions please let me know.

I have a M110 6 cyl 2.8 K-Jetronic that is showing a steady 10-12 inches Hg, instead of the expected 18-20. I can't find any inlet side leak. I've pulled the hoses for the tranny and locking and capped them - no change. I've set the timing, mixture - no change.

Can worn valves produce this? A compression test reveals low-ish compression, but is this enough to give half the vacuum? Am I missing something obvious?

The car is down on power, most noticable at low revs.

Any ideas? Much appreciated.

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'79 280SE
'87 560SEL
'83 280CE
'01 Nissan Micra
'98 VW Passat
'83 911 turbo