No acceleration? RR Classic

My friend has a 1990 H reg Classic which has developed a strange fault?
If pushing gradually on the throttle pedal the car behave's fine but if you put your foot down sharply as to get the auto box to kick down, the engine revs drop and there is no power from the engine? as soon as you take your foot off again and ease off the throttle it accelerates slowly again?
Could this be a fuel/Air problem or something more sinister?

Help grately appreciated i'm stumped!

Sounds like a possible throttle position sensor fault, or less likely an air flow meter fault.14cux systems are fairly simple and robust so having a list of factory values and a good multimeter or better still an oscillliscope should quickly tell you whats wrong.Just check all the ignition components are up to scratch as well before you get too carried away,as a weak spark will cause similar issues.

Chris I have a similar problem, 3000-4000RPM if the throttle if fully or nearly fully open the engine will die as if the ignition has been switched off, once the RPM drops to bellow about 3000 or you back off the throttle it will run normaly again. It has been like this for about a year, as I do not often ask the engine
to work this hard I have not spent much time on the problem. Fueling is good,I think it may be the coil breaking down or the amp. let us know how you go.

It might be throttle body sensor but it sounds to me like both of you have got ignition problems, check rotor and distributor cap and make sure the electronic module inside the distributor is spaced correctly. Those fuel injection systems are bullet proof and does not usually give trouble.