Check the single lead on the temp sender on the back of the head this can sometimes cause starting probs.
Also have you checked the injectors to see what the spray pattern is like also wether they are leaking at the nozzle .
Have had similar problems on other VAG cars with K-Jet system.
If they are left over night or over a few hours fuel leaks out of the injectors into the cylinders making them a right sod to start due to excessive fuel You can try unplugging the cold start injector to see if it makes a difference (less fuel) but ultimately you may find that new injectors will sort it .
Hope this helps
