I have an '86 vanagon which has been running slightly erratically (+/- 75
rpm) at all speed ranges. I ran a fuel pump output test and the pump
tested within range, and ran quietly. But during the test while pumping
the gas into a glass beaker, I could see a fine, constant stream of pin-
head sized bubbles coming out of the return hose--I'd guess 10-15 per
second. I pumped 2 extra liters to check and the stream of bubbles stayed
constant. I'm guessing that the bubbles could cause the surging I've been
experiencing as injectors pick up the air bubbles and the air/fuel ratio
fluctuates and the oxygen sensor and idle valve struggle to compensate.
Make sense?
   The gas tank is a new aftermarket tank with a 12mm output from the
pickup screen to the pump, so I doubt that the pump is fuel-starved. I'm
running a new large stock Bosch filter after the pump, not using small
square pre-filter, which was supposed to cause problems.
   Could the fuel pump be cavitating because of age?  Is this typical?
   I'm running an I4 engine, not the wbx-er, but I don't think that bears
on the issue.

       Thanks in advance for help, and thanks to the list!    Sam Payne