1996 Jaguar XJ6 4.0 Litre Base, 43000 miles

While driving, this car, suddenly accelerator pedal becomes very hard to push and car will not move at all even if you press hard pedal to the floor( Requires a lots of force). If I put brakes on, shift the transmission to reverse and to then to drive, it will start moving again. No check engine light comes on and there are no codes stored in computer. This never happens on cruise control. Car starts flawlessly even on cold morning. Battery is new and charging system works fine. Spark plugs were changed at 30,000 miles so also direct ignition coil on cylinder No.3
Any suggestion would be greatly appreciated.
Hershey 1

Sounds as if the throttle plate is sticking. Open the throttle plate and clean it with throttle body cleaner. Clean the back side of the plate and the seat where the throttle plate flap sits against.

It sounds like this car does not have an electronic throttle

Besides the dirty throttle body, it’s also possible that the throttle cable itself is hanging up within its sheath

" it's also possible that the throttle cable itself is hanging up within its sheath "

+1
It may be necessary to replace the throttle cable, and I just hope that the OP is able to locate a replacement cable for this car.