I would double check vacuum. Check EVERYTHING. The economy gauge is actually just a glorified vacuum gauge. The fact that it is at 1/2 *could* indicate a vacuum leak. Of course it could be something else as well, but I'm inclined to think you have a vacuum leak somewhere. Bad bearings have nothing to do with what you're describing. As for the compression and timing, just check them to rule them out.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280