D5 strange high idle

[Tony500]

After a week away I’ve come home, taken he xc90 to a takeaway that’s around 4 miles away all good no problems... popped into shell to fill her up then head home. The last mile I drove home I noticed at junctions the car sat around 1200/1300rpm and when in drive when slowing down felt like the car wanted to shoot forward!
Went to reverse into my drive and it won’t select R but still goes into drive? Taken for a spin again and turned off for around 2 mins with the keys out the ignition and doors locked.
Started her up and all was fine? Managed to get Vida working and plunged it in and shown no errors?

What could cause this?

My rear engine mount is gunned and have a new one in the garage waiting time to get fitted but the pipe is removed and I’ve put a straight barbed connector where the T price was at the front of the engine.

I don’t think it was a vacuum leak as it would die a little when in gear and footbrake pressed?

This is the second time in 5 months this has happened and no errors?