Just after thoughts to what people think of some advice i got from local
saab garage (not dealer - private specalist uk).
The check valve (oneway valve) that sits on the breather hose from the inlet
manifold and the cam cover, apparently is of no use and does not matter if
it is there or not.  They removed it and didnt replace it.
This was some time ago and i never noticed a difference, however i have
known for a while the dump valve needed replacing and when i did replace it
last week with a bosch standard dump valve I started having problems.
The check engine light flickers when i come off boost quickly.  Also
replaced all old crummy vacuum hoses with nice new silicon ones *bling*.
My idea was that the extra boost that the new dump valve was not leaking
might be finding its way into the top of the engine and causing the warning
light flicker.
This probably exposes me as a rank amateur with no true idea about my engine
but you've got to learn somehow!

so should i refit a check  valve and could this solve this problem. if not
any other more ideas?

Thanks Derek

PS the garage has just gone bust its a shame the mechanics were nice and
helpful.