Is your car chugging during normal driving/operation? Mine only does it for 2-3 seconds, when it's restarted after already being warmed up. Normal driving is fine, idle is smooth, and performance is generally strong.

With regards to parts... I haven't bought many myself, but have used Autodoc and AwesomeGTI in the past. Both recommended. Autodoc is often cheaper that garages quote for parts, but takes 2-3 weeks for delivery to the UK.

Been using https://www.partsinmotion.co.uk

There prices and delivery are pretty good apart from random things that incur a delivery surcharge as I am in Inverness. If its skoda genuine parts then probably dealer or there is https://www.skoda-parts.com/ as well as https://www.lllparts.co.uk/ who also have original manufacturer parts diagrams and you can narrow it down with VIN.

Alasdair

Car back from the garage. The startup chugging was nothing to do with the diverter valve, and is still present after the GFB DV+ has been swapped for a 'Rev G'.

So... I'll likely live with the startup chugging and rattling until its next MOT, and get the timing chain/tensioner replaced, if there's nothing else major that needs doing.

The 'Rev G' seems a bit smoother than the GFB DV+. I haven't yet driven it enough to say whether I prefer it on not - "subtly different", rather than "better/worse". The performance is still there, but it feels smoother in its power delivery now, rather than the torque/boost all arriving in one big lovely lump.

And as for the lift-off/overrun jerkiness... the engine mount and upper+lower gearbox mount needed to be replaced. They said that the engine mount was 75% worn, and the others were showing signs of aging. I'd already had the lower dogbone mount/bush replaced earlier this year, so that's now all of the mounts done. Jerkiness gone and the lift-off and gear changes feel sharp again.

@SinisterKid97 Sorry maybe missing stuff reading on a phone. But who did the Stage 1 remap, and what is it, bought generic or a custom map? Is the car running on E5 97 or 99 minimum Super Unleaded?