ford puma problems

[simon mk2]

Can any one help?

I have a 1.7 ford puma and when it is underload at 1700 rpm the car jurkes as if you have changed gear to soon (only at this rpm anything under or over and not a problem).

I have checked the plugs and leads and they are clean.

is there any raeson for this and will it get worse?

any help will be great

Thanks Simon