You could do a check to see if the clutch is wearing out and/or is engaging--if its anything like MBs you can supply voltage to engage the clutch. Not the greatest starting point but until you have gauges its going to be pretty tough.

__________________
TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth