I have had a lot of work done to the engine of my 420. New head gaskets,water pump,fuel injectors and fuel filter with new hose. No more heavy oil consumption or slow take offs now. I have taken the car on one long trip to North Carolina (i live in philadelphia). The 420 ran very,very well and i was impressed to say the least.My problem is that i'm still haveing rough idleing at start ups and rough idleing while stoped at red lights. Should i buy better plugs and wires or check the air hoses. I'm just stump at this point. While on the road the car runs like a dream, it's just the rough idleing and sounds like it's missing, dose anybody have a clue? Please let me know!