The Vanagon owner manual states that flickering of the light is ok at idle.
My 85 never did this until the oil sender on the left side of the car
started to leak and was replaced.  Over the next 3 years it got
progressively worse until it was on at all RPM's below 1800.

Finally broke down, removed the tin, and low and behold, found that the
wrong switch had been installed (can't remember the specifics, but it was
not the same as provided by the dealer to replace it).  Swapped switch,
never had the light problem again.  Of course I turned prematurely grey
waiting for the engine to seize.

Last I heard, it was still running with the guy I sold it to in FL.

Scott