I've put in new leads,plugs and cleaned up the dizzy but still get a slight missfire on idle, it doesn;t seem to want to tick over smoothly. i've run injector cleaner thru it too with no results. when driving it seems fine but drinking fuel more than usual and this morning on a cold strart a puff of white smoke came out the exhaust but has been fine since.

Any one got any suggestions?

its an 89 glt

White smoke isn't indicative of much IMO, usually just cold weather and condensation in the exhaust gas (petrol burns to make some water amongst other things). Possibly weak mixture I suppose.

More likely to be fuel I think if no other symptoms and good spark;

Leaky cold start injector or other injectors (more likely black smoke due to rich)
Wrong mixture due to air leaks or wrong detection of air (AMM faulty).
Faulty cold start throttle bypass thingy
Poorly closing/dirty throttle body
Fuel Pressure regulator problems

Most common is air leaks due to split pipes, check the bypass pipes behind the throttle body particularly.