Sounds like you may have a failing fuel injector. If you have an emmisions check done, and your Hydro carbons are at a high level on idle,then that's where your problem lies. I has the same thing, low miss fires on cyl 4, rubbish on cold start up, would chronically misfire for the 1st 60 seconds from cold, then would improve whist it warmed up, though on live misfire check, it would show a problem on that cylinder. It wouldn't show as an error on VCDS if it was an injector.