Sam,
I have never heard anyone ask this question before. Try looking at the
spray pattern of one injector and report back.
Does the surging occur if you unplug the O2 sensor?
Ken Lewis

On Thu, July 15, 2010 5:22 am, Sam Payne wrote:
> 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
>
>