Avionicsbloke - all noted, thanks. We flew on Monday and everything worked fine. The suction is just over 5, where it usually is, (about 5.25). The only other thing, which may or may not have had anything to do with it, was that P1 adjusted the DI before starting the engine. Could this have 'confused' it, I wonder?
Anyway, all the comments are much appreciated, and we will keep a close eye on all parameters and act as and when anything changes.
RF.