To echo Joel's comments about Techron, etc.....my usual method of
adding Techron, or any fuel injection cleaner, etc.  is that
if I am going to be going on a long drive, especially where I
will be consuming at least 3/4s of a tank of gas, I'll toss
in a bottle of FI cleaner (or two) when I top off, and off
I go onto the highway.

This way, I know most or all of the cleaner is going out the
exhaust. This technique has served me well on the GTI (215k miles),
and I do it on the EuroVan. I don't think the EVs injectors
are dirty....but what the hell...what's a little preventitive
maint. once in a while.

Ric