Rough idle when cold

[Passat my07]

Hi everyone,
I’m trying to fix a rough idle when cold on my brothers 1.4 twin charger gt.
I scanned it with a launch scanner and nothing came up. When you take the oil cap off the idle is the same making me think it’s an engine breather system fault. It doesn’t seem to have a normal pcv like a gti engine. It does have a check valve fitted in a hose on the timing chain cover so it could be that? Could also be carbon build up on the inlet valves?
Has anyone had an issue similar to this?
Thanks.

[brad]

Inlet valve carbon.
Buy a $20 endoscope and feed it into the inlet to check

[Passat my07]

Thanks. I’ll try to find somewhere to feed it in. It doesn’t look like much fun to remove to give them a proper clean.

[brad]

I think there's an inlet air temperature sensor at the front.

I haven't done a twincharger but on the EA888 block the R&R isn't hard. The actual cleaning is time consuming.

Why not try one of the chemical cleaners and see if it improves slightly (it won't fix it). Subaru Upper Engine cleaner is good.