I have a problem with the engine on my 85 Vanagon GL "stumbling" or
misfiring on an intermittent basis.  It usually misfires or bucks once or
twice and then runs fine for a while (10-20 minutes).  Other than this
problem the engine runs great.  (This van has 194000 miles, with about 15000
miles on a replacement, VW-remanufactured engine).

I have tried to determine if it occurs under particular conditions (cold
engine, warm engine, cruising, accelerating, etc) but can't be sure.
Although it does seem to occur only when driving -- it never occurs or is
not noticeable when idling or acclerating in neutral.

Does this sound like the air vane resonance problem which is fixed by
replacing the cable to the air cleaner assembly? I don't have that cable
installed, but never had a problem like this before.

I have changed the plugs (D7CC), checked all vacuum lines, and checked all
grounds and electrical connectors I could find.  Air filter was replaced <
15000 miles, gas filter replaced < 5000 miles.  Spark plug wires,
distributor cap, rotor, and hall generator were replaced about 25000 miles
ago; cap and rotor still look good.  Ignition coil, FI computer, and fuel
injectors are original.  Fuel pump is original.  

It's too hot here for water in the gas to be the problem.  (Also I had that
problem a few years ago and it didn't act like this.)  Possibly vapor lock?
Except that the van starts and idles OK, yet the engine will misfire or
stumble after being driven for a considerable time.

Any suggestions regarding possible causes or additional things to check?

***  John Clavin  |  Austin, TX  |  jjc@bga.com  ***********************