sworkscooper

Is your Mini SPI or MPI, single or multi point injection? If it's post 96 it could be an MPI. The MPI has a reset that you can do to try and sort out the idle air control valve / stepper motor. If it's an SPI I'm not so certain as the inlet manifold is different. SPI has two pesky vacuum pipes with stupid rubber elbows that can get broken off by the ECU and under the throttle body and if this is the case the mixture will be screwed, and tick over will be high. If the car is MPI you simply turn on the ignition for a few seconds, then turn it off and with the ignition off press the accelerator pedal to the floor five times. Then turn the ignition back on and start the engine. If the car has been off the road for a while, it may be that the IACV will need a good clean as they can get a bit gunged up. Pscan can help to reset it but please tell your mechanic guy NOT to adjust the idle speed using the throttle body screw as these are set from the factory and should not be moved ! Also, worth mentioning is the throttle cable tension on the MPI. The cable should have some slack/free play in it where it goes to the throttle body. The cable is anchored to a bracket by a square nut. If the cable is tight, simply lift the nut off the bracket and back it off till you have no tension and slot the nut back on the bracket.
If you buy a Pscan you will need to tell Phillip which engine the car is as the diagnostic port is different. The MPI diagnostic port is under the dash and the SPI in in the engine bay and should have a black rubber cover over it. 16 pin vs 3 pin I believe.

John

PS Just checked and Japan spec Minis were all SPI so check those stupid vac pipe elbows!