I got an old Trek of ebay that came with Campy parts and Phil hubs and a new IRD 5 speed Freewheel--which is awful or broken or something dangerous. When riding, after coasting a bit, I can pedal up to 3/4 a rotation OR MORE before the thing catches and I start pushing myself (super scary in traffic!!).
flush it out by tilting the wheel to the side with the freewheel up. Squirt some lubricant in where the freewheel rotates as you spin it. I use a polymer lubricant. I'm sure other things would work. If that doesn't fix it, replacement is necessary.
'''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
Probably sticking pawls due to dried out lube. As jeepr sugested, lay the wheel on it's side, freewheel up, and dribble light oil into the seam between the rotating outer shell and the inner fixed core. Rotate the cogs while doing this to distribute the oil. Unless something is broken inside, that should free up the pawls and make it work properly. If the oiling doesn't fix the problem, a new freewheel is required.