Anti stall rpm not dropping back to normal

[isc555]

Hi, got a 2014 A4 2.0diesel Allroad. It used to idle at 800rpm and then rise to 1000rpm when 1st engaged to set off. It now constantly idles at 1000rpm never dropping to 800. Any ideas? Thanks.

[Crasher]

A code read is the simplest first step

[Renars]

Could be active DPF regen or if it has one - electric auxiliary heater core working (but its doing it only if its cold)