I recently changed the timing belt, cam & crank seals, water pump and thermostat in my GC8. I made sure I followed the instructions to the letter, and the crank and timing marks were perfectly lined up. Since then the car has had a rough idle. Shakes quite a bit in the car when sitting idling. It has not stalled in the 50kms I have put on it since the belt change. Just a rough idle. When I did the timing belt, I noticed that the belt was out one cog (thanks to the dealer servicing) on the exhaust on the drivers side. I corrected this and made sure they were perfectly lined up.

The car revs fine and has no strange knocking noises. A bit of belt noise. It is slightly sluggish, and seems to have a tiny miss before boosting.

The car is stock as a rock. No modifications at all.

Any ideas what is causing and how to fix my lumpy idle?