Land Rover Repair: Range Rover P38 97 fast idle, obdii scanner, air flow meter

Question
My P38 will idle upto 2500 revs when I start the vehicle up. I have changed the throttle position sensor and idle stabilization valve recently and this seemed to cure the problem for about 2 weeks. It has now started to rev up again. Do you have any ideas what the problem could be and how I can rectify it? Would changing the air flow meter have any effect on this?

Answer
It is unlikely to be the air flow meter, which is a very expensive part, as well.  If it was an air flow meter, you should be able to see a code with anny OBDII scanner. It is more likely that you need to have your adaptations on your ECU re-set and have your base idle re-set. This has to be done with a factory compatible diagnostic tool (not just a generic OBDII scanner).