Mystery

Howdy,
My diesel Rabbit has been purring like a kitten, but today I had a heck of a time starting it, and on the way home, the engine suddenly over-revved severely when I stopped at a sign. Turning off the key didn't help; had to slip the clutch to kill it. I checked the oil, (quart low) coolant, (full), water temp., (normal) and throttle cable (no binding). I started it up, and it seemed to run on 3 cylinders, sometimes 4, and ran bad, with a nasty, smelly smoke, all the way home. Didn't smell like diesel smoke.
What have I done now?:banghead: My thoughts are: Blew a head gasket (white tinge to the smoke, and it smells funny); injectors? Injector pump? timing belt slipped a tooth? Demons?:evillol: I have limited tools, and little motor experience, but I'm not a-skeered. Any thoughts?
Thanks,
Steve