I used to try to get my wife to put isoproyl alcohol in her old Fiat.
She never could pass emissions without radical performance robbing
adjustments.  She never would try it, but my reasoning is that the
alcohol  is clean burning and using just a gallon on a nearly empty tank
would pass emissions, clean the injectors and do no harm  if topped off
with gasoline promptly.  I drive the diesels so never actually had a
chance to test this.

Ed Lowe
82 diesel Westy
85 Golf diesel
92 Cabrio