Klaus,

Again, I am profoundly thankful for your tireless concern...

I think I finally figured this out. After weeks of reading old posts from a variety of sources, I stumbled into a brief discussion where a person recalled reading a TSB, or Technical Service Bulletin regarding a 1993 Volvo 850. It seems that when the 850 engine was designed, the coil wire to the distributor passed too close to RPM sensor wiring. As a matter of fact, a while back I replaced the distributor cap, rotor and wires and probably messed things up.

At the time, I didn't pay any attention to the routing of the coil wire. Apparently my coil wire ended up too close to the RPM Sensor connector and started arcing across. Hence, the intermittent RPM sensor signal, and that horrific bucking I described.

As a test I used a piece of rope to maneuver the coil wire further away from the RPM Sensor connector. I haven't had a buck or misfire in days. Upon examination, I could see an area on the coil wire that had evidence of the spark escaping to ground.

If more 850 owners were aware of this TSB, they might save themselves money and a few headaches.

I'm still a little concerned about my mileage, but my big problem appears to be solved.

You're in more discussions than me, so maybe pass this info along.

Thanks again!

- thumbs