Think I may have finally found the root cause of the random poor running.
For some reason the ECU fitted to my 56reg 2.2 Signum is actually from a Vectra.
Although no error codes or MIL lights the ECU is reading or trying to read EGR values.
From mid/late 2006 the EGR was deleted.
Trying to find out if the presently fitted ECU can be reprogrammed/refurbed with correct info or do I have to get the listed part??