had astra since nov...it had new egr valve cos the old 1 faulty and had noprobs.then driving home from a different job site i been stuck in stop go traffic for the past half hour.only done 5 miles.the engine manangement light has just come on.the car is using a bit of oil and you getting some go in to the throttle housing pipe etc....any ideas why it come on...doesnt seem to drive any worse than this morning