Hi there,

That happened on my xr3i (90spec with efi engine). I changed the plugs, leads, mixture pot(on inner wing), cleaned the idle control valve, air filter, all to no avail.

The result was that the throttle stop bends on the throttle body, try opening it a couple of thou, by bending it slightly and im pretty sure that will fix. It doesnt cost you anything either!! I think they just bend after thousands of throttle opening and closings.