Take top off injector housing, large black shaped disc on top of engine. Think it's held in by 2 or 3 torx head bolts. Take it out & clean, then replace. If replacing for a new one, use a genuine Vauxhall part. Think they're about £45 off flea bay.
You can't blanc off the egr valve on the spi models, I haver one too.
Have you got an ecu light illumination?
This forum will help:- http://www.vauxhallownersnetwork.co.uk/forumdisplay.php?f=83
George., December 2008
