My 2007 wrx has been surging the last few times that I have driven for more than 2 hours at highway speeds. The last two times I had the Cruise Control on for more than 2 hrs at 70mph when all the sudden it begins to surge when trying to throttle(i.e. when CC attempts to compensate when I start to head uphill or into a strong headwind). From that point on, the car will continue to surge as well as suffer from an increase in lag time. I have pulled over at a rest area, waited for half an hour, and the problem continued. However, after letting the car rest overnight the problem ceases until the next time I drive for 2 hours or more at highway speeds. The car has 55k, always runs 91 octane, and Royal Purple 5w30 (which is replaced along with filter every 3000 miles). There are no modifications to this vehicle.
Any ideas on how to solve this problem?
Has anyone else had similar issues?
Also the Check Engine Light hasn't turned on when this occurs.