Mine used to do this as well - stock BA F6, no injectors or tune. Idles OK after starting up for about 20-30 seconds, then turns into a thing that sounds like a V8 with a huge cam. Sometime sorts itself out after about 10-15 seconds, a bit of a rev up without me touching throttle (to about 2000 rpm) then good again - smooth idle. Mine started doing it only in the winter last year, it then went away in the summer. Came back this year when the weather got cold again. This year the car started to occaisionally stall, and the 'check engine' light would come on. Turn off igintion and restart = all good. NOW FIXED! - change your O2 sensor! I think the reason it happens is that the O2 sensor takes a while to warm up (or something). That's why it's worse in the cold weather. My service guru (yes Ford do have some!) told me the reason it didn't happen straight away after starting is that the cars ECU doesn't go into closed loop fuel control until the engine has run for a few seconds (like about the same time it took the problem to start!). When the ECU switches to closed loop, if the O2 sensor isn't warm (ready? - or whatever the issue is?) then it plays havoc with the mixture (A/F ratio). This made complete sense to me because it happened every time at the same time after starting (switching to closed loop). I think the car runs lean, and that causes it to run 'lumpy'. If I tried to drive through the problem, even at light throttle openings, the car would really struggle to generate any power, until it cleared itself (all of a sudde with a real spurt!) ...anyway - mines been good for two weeks now - no issue at all! - smoother idle than new! Check your O2 sensors - that's my only tip. (By the way - The service guys had already tried changing my TPS and this didn't fix it at all) Hope this helps somebody???!!!