Reduced idling speed after dealer visit

[Tony B]

I have just got my 2012my, 6mt E92 back from the dealers following further attempts to address the constant speed resonance that first started to appear around 4000 miles.

I will not go into the details on this but they did replace the transmission and clutch at about 7000 miles and this seemed to have cured it, but in the last few weeks it seems to be coming back again.

Anyway, since I got the car back, the idling speed when warm/hot has dropped by about 200rpm from 750 to 550, when in neutral and foot off the clutch. Depressing the clutch sees the revs go back up to a constant 750 again. Its almost as if there is a major drag from the transmission.

The obvious thought I had was that maybe they had put in a higher viscosity transmission oil, but if that was the case, would not the idle speed control software keep the revs constant anyway?

I have not been able to speak with the tech yet as he has been off sick this week. Before I picked the car up he did say that they had slackened off and re-tightened all the fixings associated with the driveline in case there had been some misalignment.

Anyone else had this reduced idle speed symptom, clutch up v clutch down, when stationary and in neutral?