Volkswagen Repair: Erratic Idle when warm, vacuum leak, dognuts

Question
Hello Ryan, I have a problem with my VW '87 Cabriolet 1.8L
8v.  I have noticed that when ever the car gets up to
temperature the fuel injection( under the hood) starts to
make a hissing sound like "zzzzzzzzz" and the idle goes up
and down like it wants to shut off but stays on.  As weird as
it sounds, the noise sounds nice like a turbo, but no turbo
here. and it gets louder with high RPM's and vice versa.  I
have changed the fuel filter and sprayed the fuel injection
with cleaner but does it again.  Could this mean a new fuel
injection?  Please help, thanks!

Answer
I had an 84 cabby that did that made the same noise and it turned out to be the main fuel pump, it makes that noise because it is starving for fuel.  Could also be a vacuum leak, there are little rubber dognuts around the injectors that go hard and crusty after so long and they begin to leak air.  I would start by putting in some high quality fuel injection cleaner in you gas tank and see if that will clean out the pump.  Keep me posted.

Good Luck,
Ryan