My car has developed a problem over the last few months that I cant get to the bottom of.

The car is really hard to start when cold, I have replaced the battery, alternator, camshaft position sensor and crankshaft sensor.

None of these have made a difference, when the engine is warm it starts perfectly.

Now there is a vibration/misifire on warm idle, every 10 or 15 seconds, but it doesnt do it all the time, revs are not fluctuating, but when the fans come on the vibration disappears.

Has anybody had the same issue?