I've got a strange problem, my engine light comes on when I sit on or just over about 115km/h but it will go off if I slow down for a few mins or speed up towards to about 170 and the slow back down again.
A friend thinks that its just a slow down warning but I'm not sure.

I've checked the error codes and nothing is wrong and the car runs perfect as I'm a freak about reliability and check over it on a weekly basis.

any help is greatly appreciated.