This problem started originally while driving on the motor way, after going over 100kph my car would start shuddering intermittently. So I automatically suspected that my spark plugs needed changing (ngk platinums), after changing them, a week later the car now suddenly loses power intermittently when changing gears in normal traffic. I may be on second gear then change gears & suddenly theirs no power as if tha petrol is struggling to surge through the system. The engine now occasionally turns off while idling (at the lights). Does my car need the timing adjusted??? It maybe useful to mention that my car is a 4wd turbo, straight 6, fuel injected & 24 valves.Please can someone help me!