here's some poop from vw that might interest those already interested in
which gasoline to put in your bus ..

from Service Bulletins, Model Year 1990
.......................................................................
Technical Bulletin
Group:    20
Number:   20-90 T01
Date:     May 31, 1990
Subject:  Improved fuel additive  ZVW 239 003
Model(s): All Gasoline Engine Vehicles

Research by Volkswagen AG and other manufacturers has shown that the
performance of todays gasoline engines is directly influenced by the
type and quality of fuel used.

Fuel without the proper additives can cause deposits to collect on
fuel injectors, intake ports and valves.

This build-up of deposits can cause the following conditions:
     * unstable idle                    * power loss
     * surging                          * engine run-on
     * misfiring                        * pinging/knocking

Extent of deposit build-up varies depending on type of fuel used,
operating condition, etc.  Refer to current Technical Information
Circulars for description of deposit grading system.

PREVENTION
Prevent deposit build-up through the use of gasolines with injector
and intake valve deposit control additives.
Consult the suppliers and service stations in your area about fuel
grades and additives that prevents or removes these two deposits. <sic>

In areas where gasoline containing deposit control additives are
unavailable, light deposits can be controlled as follows:

* add one 6.5 oz. bottle of Autobahn Gasoline Additive,
  P/N:  ZVW 239 003.

Note:  Fill fuel tank completely.  Do not refill until fuel gauge
       reads 1/4 tank or less.

REMOVAL
Moderate to heavy deposits can also be removed with Autobahn Gasoline
Additive, P/N:  ZVW 239 003.
When used as follows this additive has shown to be effective.

* Check fuel injector spray pattern.  Purge injection system with G-16
  cleaner.  Refer to current Technical Information Circulars for
  injection purge instructions.

* Check that fuel and ignition systems are within specifications.

* Add three (3) 6.5 oz bottles of Autobahn Gasoline Additive,
  P/N: ZVW 239 003 for each of three (3) consecutive fill-ups or
  1000 miles.

Heavy deposit concentration may require 2 or 3 cycles of the above
treatment.

Note:  Fill fuel tank completely.  Do not refill until fuel gauge
       reads 1/4 tank or less.

* Deposit removal with Autobahn Gasoline Additive, P/N: ZVW 239 003
  is more efficient with engine at operating temperature and at
  moderate speed, short distance driving conditions.

* Because of possible contamination of the oil,  the filter and oil
  must be changed at the conclusion of each removal cycle.

-----------------------------------------------------------------------
Technical Information
Group:    20
Number:   90-02
Date:     March 31, 1990
Subject:  Gasoline containg detergents
Model(s): All Vehicles with fuel injection

Volkswagen United States, Inc. recommends the use of gasolines which
contain 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 of sparkplugs, stlling and rough engine performance in
vehicles with fuel injection systems.

Because many of our customers may not know whether or not a particular
brand of gasoline contains these detergents, we have examined
advertising literature published by gasoline refiners and other publicly
available literature discussing gasoline ingredients.

We cannot independently confirm the accuracy of gasoline advertising
claims.  The brands of gasolines listed below are claimed by their
manufacturers to contain detergent packages designed to keep intake
valves and fuel injectors clean.  There may be other manufacturers that
offer similar detergent packages.

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.

   Amoco:                  All grades
   Arco:                   All grades
   Chevron:                All grades
   Citgo:                  Some grades in early 1990
   Conoco:                 Some grades in early 1990
   Diamond Shamrock:       Premium grade only
   Exxon:                  All grades
   Fina:                   All grades in early 1990
   Hess:                   All grades in early 1990
   Marathon:               All grades
   Mobil:                  All grades
   Phillips 66:            All grades in early 1990
   Shell:                  All grades
   Sunoco:                 Premium grade only
   Texaco:                 All grades
   Unocal:                 All grades
   Hess:                   All grades in early 1990
   Hess:                   All grades in early 1990