Being a 'lightfooted' driver, I have very rarely floored the pedal and have been considerably startled when I have done so !
I decided that it was due for a test, result, flat as a pancake, it got there but, slowly; 'oh dear' I thought cracked vacuum reservoir since various threads on this forum imply that this is the usual cause.
Taking off the cover plate on top of the induction manifold reveals the vacuum switching solenoid which operates the manifold flap valve.
Pulling off the pipes and sucking convinced me that the reservoir was OK and holding a vacuum.
Then I noticed a pipe hanging free under the extreme rear offside branch of the manifold, ah! easily fixed, but no, the short section of rubber pipe that this plastic pipe pushes into was split.
What you have in this area is the vacuum take off from the inlet manifold has a small rubber elbow with a 'T' connector, one side going to the reservoir and the other going to a capsule on the fuel rail; the short section of rubber hose on that side was split also.
I assume that the capsule on the fuel rail has a spring loaded diaphragm which gives extra pressure to the fuel rail when the vacuum disappears ( wide throttle opening ) and thus gives a richer mixture for acceleration ( I stand to be corrected on this, but it seems logical )
The two short sections of pipe that had split seemed to be in perfect condition other than they had split !! replacing them was a sod due to the very restricted access in this area.
By removing the fuel rail pressurisation, this small fault had not only reduced the normal acceleration to be expected but totally lost the dual ram 'kick' and by giving a small but continuous air bleed into the rearmost manifold branch would have unbalanced the air/fuel ratio mainly on tickover for the rear cylinders !!
Everything is now back to normal with the ability to frighten myself fully restored.
Edit.
I subsequently found that there is a rubber elbow on an actuator between the heater blower motor and that had also split.
This does not cause a permanent loss of the vacuum; only when the air recirculation switch is operated, which could be a bit baffling
