I have a bog standard 1.8 16v Club on a facelift T-plate Vectra which regularly lets the revs go below 500 when I dip the clutch (and I think it's only when braking too but not sure). You feel like it might stall but no lights on the dash appear and it corrects itself fine.
I've had the throttle body inlet cleaned and I'm told it's on the newer 1800 engine with no faults recorded on the Tech2 but I'm still at a loss.

Anyone any ideas ?