I'm having an intermittent problem with the above vehicle quitting while driving. Initially this was mainly when the engine had been working hard; i.e. prolonged climb at the low end of the RPM range. Now it's beginning to happen more frequently and under a variety of conditions. When it stops if you let it set for 10-15 minutes it restarts and drives fine for an undetermined period of time (now getting shorter). I've replaced the fuel pump, fuel filter and most of the hoses on the fuel and intake system. Any suggestions on where to look will be greatly appreciated.

I've also found that the auxiliarry air regulator is not full closing when it's warm. VW says that this part is no longer available. Any suggestions on how to by-pass this part or other work-arounds.