Ok Volks.. 
While searching through my database of TSB*s for a fellow listee for something else, I found this one about fuel for the Vanagon.  When reading this, please note that *driveability problem* is VW*s euphuism for engine hesitation:

"Technical Service Bulletin No: 90-02 3/31/90
Models Affected: All
Subject: Gasoline containing detergents

VW US Inc recommends the use of gasolines which contains detergents to keep intake valves and fuel injectors free of deposits.
Gasolines without detergents tend to clog fuel injectors and leave residue on intake valves which can cause unstable idle, surging, misfiring, stalling and rough engine performance in vehicles with fuel injection systems.
[usual legal disclaimer clipped]
Please pass this information on to customers who have experienced driveability problems that may be caused by carbon deposits on intake valves or fuel injectors.

The following are brands of gasolines with detergents:
Amoco, Arco, Chevron, Exxon, Marathon, Mobil, Shell, Texaco, Unocal: ALL GRADES
Diamon Shamrock, Sunoco: PREMIUM GRADE ONLY
Citgo, Conoco, Philips 66: SOME GRADES - ask
"
So, if you haven't been using detergent gas, start using it.  And clean your engine often with injector/valve cleaners.

Happy Vanagoning!

Yau-Man Chan
87 GL