Lag in Xantia Throttle Response

[Peter Mann]

My 2 litre injected 1994 Xantia ( 50,000 miles) has a throttle response unlike older Citroens that I have driven, in that the
engine revs are a lot slower to rise after application of throttle. This slow throttle response not uncommonly catches me out on
stationary starts, with the engine stalling as the clutch engages while the motor dithers and mumbles.
Another curious difference is that the engine revs decrease much more slowly when releasing the throttle (as in gear changes).
I understand that some damping of engine response can contribute to overall smoothness when adjusting throttle to shed or add speed, but this seems excessive, and makes for a slow gearchanges when matching engine and gearbox speeds to shift gears
(reduces wear of the clutch friction material).
And sometimes when we are doing a little low flying with engine fully warmed up (70 mph in 5th, 3500rpm), a small increase in throttle to compensate for slope will trigger a momentary stumble, like the fuel or spark has dropped out for about half a second. Ugly. Real ugly.
So far as I know, none of the engine management components have been replaced since new (excepting maybe the sparkplugs).

[Sl4yer]

Have you checked / changed the fuel and air filters? Those could cause some odd running and poor responses if blocked.