Hi, just hoping someone has any thoughts on a rough running issue. The car is a 2015 Astra J GTC SRI with the 2.0 diesel (A 20 DTH). Everything was fine before the last service 3 weeks ago, since the service the idle from cold start is rough with fluctuations of 50-100 rpm and when it's particularly bad there is a knock from the engine almost as though the timing is being advanced.

[color=#333333]The issue is at it's worst in hot weather but can occur at any time from a