[Vwdiesel] Strange IP Problem

[James Hansen]

I have to go with the air in line philosophy, or a fuel restriction Val.

Real bugger to find too... an intermittent air leak in a fuel line.
I'm not envying this in the slightest. BTDT.
return lines are all good too?

Try tightening up the recirculation valve on the top of the filter- 
stuff a toothpick under the hairpin that holds it in, just to make it a 
tad tighter.  I had a jetta that loved to leak air into the system 
there: no toothpick, it sucked air, with toothpick, it ran fine.
-James