the car occasionally cuts in to limp home mode .. .the problem is only happening maybe once a month but when it happened last time the driver was on the motorway so shes not happy !!have code read and the only fault showing was po500-74-- speed range performance -not really convinced that could be the cause of the problem- egr system is so clean you could eat your dinner off it tyres etc all even same brand have done some research it seems to be fairly common on this model but cannot find any posted solutions anywhere ..any suggestions?.its done around 66000 miles