Got a problem with my 94 fiesta rs1800 and no one can find what the problem is with it.

It starts to vibrate/shake the whole car (believe its from the front end) when you accelerate,but as soon as you back off the accelerator all is fine
The car does feel a bit unstable when going around tight corners etc.

It has got Deflex gearbox mounts fitted but they seem to have no movement in them at all so it looks as if they are fine.
Checked all tyres.

Its down at a mates garage now and he says the only thing he can think of now is the diff in the escort rst gearbox

Think im close to burning the thing now