2005 XC90 2.5L Surging while crusing

[WellingtonX]

Dear All,

The XC90 has 148,000 km on the clock. I have had quite bit of trouble with check engine light and codes over the years - PVC change, throttle body clean etc. I recently changed the turbo solenoid and this made a significant difference. Where I was getting the check engine light perhaps once every two weeks, I get it now once every 2 months but its still there. Check Engine Light and Engine System Service Required Altert both came on again yesterday and I noticed something new while driving. Cruising along at 80 km/hr, sitting on 2,500 rpm the engine was surging upwards by around 300-400 rpm and then returned to 2,500 rpm. This cycle repeated perhaps every 5 seconds in a very repeatable pattern. It also seemed to be surging at lower speeds but not as much. The fact that the Check Engine Light and "Engine System Service Required" alerts had just come on would seem to indicate they are related. I would appreciate any thoughts forum members may have.

Regards