could a faulty diverter valve cause a rough idle?

[Nate c]

hey guys, got a mk5 gti and it is running rough at idle, soon as i give it a tiny bit of throttle it runs smooth. Don't think its the pcv as ive got no vacuum on the dipstick/ filler cap. only code ive got logged is turbo underboost and has only occured twice in the last few hundred kms. just wondering if a diverter valve could cause this rough idle.

cheers,

[El_gti91]

Perhaps a coilpack issue.