Does this happen when you are moving? For instance, if I'm trundling along in mine just after starting, using the engine torque to pull me along without any accelerator input, if I then depress the clutch, the engine revs will rise as the load on the engine is released.
This typically only happens when cold and the engine is still 'on choke' with the ecu putting a richer fuel mix in (hence the power to move without accelerator input). The engine also sounds pretty fruity and tends to be hesistant.
Do the revs quickly fall back after initially rising up to about 2k?
Both my engines have done this so presume its pretty normal or is your problem different to the above? Hth