Engine begins to shake after 30 seconds of start up?

I've got a problem with my vehicle listed above 2.0l Petrol. Basically, when I start it up from cold, I leave it for about 30 seconds and the engine starts to shake and the revs go up and down ever so slightly. If I try to accelerate it's like it's trying to pull away but can't and jolts a lot even with my foot all the way down. Once the shaking is done it runs fine and won't do it again unless I turn it off for a couple of hours and start it up again. Run an engine diagnostics test but nothing comes up. I really appreciate your help! Thanks!