gf8 missing on idle

Iv done a search but couldn't find anything, basically the car is now idling like a bag of sh*t, it's missing well seems like it is, at normal revs on idle (750 ish) before it was fine, now even at 8-900 its missing and hunting revs, it's driving perfect though, no issues with boost or missing under load, not down in power from what I can tell.

'll that was done was removal of inlet mani fir painting and refitting, there was an issue with one plug to the knock sensor but that's been fixed, I think it may be the iacv but there are no error codes coming up or cel either, all vac lines are intact and correctly routed anyone got any ideas what it could be? Iv checked wiring connections and earths abs all seem ok....... I didn't use new gaskets on the mani could this be a cause?

Any info greatly appreciated, as said car drives a1 just idles like a pig......

Dan



meant to say car is stock tuned and only mods are sti topmount and apexi pod filter and a bov......

Chances are you have a poor seal between the manifold and the head
When at idle the throttle body is almost totally closed and the pistons are creating a large vacuum in there
Air will be sucked through a poorly seated gasket causing a misfire on that cylinder
It won't affect things as badly further up the revs as there is much more air flowing around compared to the volume your leaking with less vacuam involved and as its a turbo engine things will be reversed once on boost and you will be loosing a little of that instead you might hear this as a hiss or a whistling noise

Could be idle control valve