Are all six plugs intact or in the plug hole? I used to have a car that had one plug hole slightly stripped, on occassion the #1 plug would blow out. Not saying this is what she experienced, but it can happen. Also check all vacuum lines. I had one pop off near the fuel distributor, produced rough idle, poor acceleration and the economy gauge was always pegged in the red. Replacing the line on the nipple cure it all.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.