Engine revs will stick at 1.5-2k idle, help please. Makes slight rubbing noise

[Patttt]

For instance, when I'm coming down my drive to park the car in first, the revs will stick at 1.5k- 2k and it makes a slight rubbing noise/ grinding noise (not metallic as far as i can tell) However if i do this in second gear then drop the clutch to come to stand still it won't stick and idles fine at just under 1k. If i sit at stand still when the revs are stuck at 1.5k- 2k dropping the clutch doesnt effect it. I've checked the throttle cable and it's not stuck or anything. I recently had a clutch change if that's any help?


It's really bothering me though as I'm taking the engine out soon for my turbo build and i'm getting really paranoid as to why it would be sticking/ rubbing noise???

I haven't found any swarf/ ground off metal in the oil, and im not losing any oil/ coolant if that's any help either. It's driven fine apart from this problem! Only once did the oil pressure light flash and buzz at me on a 5th gear run, but after closer insepction i found the previous owner hadnt put enough copper washers on the threads of the oil pressure sensor so oil spurted out. Oil level never dropped below correct level though!

Rear gearbox/ engine mount rubber is buggered, so would this + possibly a vacuum leak cause the idle sticking and rubbing noise?

Any advice would be greatly appreciated, thanks.