I have a 1999 Intrepid ES 3.2 with 134,000 miles on it. This car has been running great but recently it has started acting weird and whenever I start it up it will idle down and starting rocking from side to side. All regular maintenance has been done it. We just changed the intake and valve cover gaskets as well as put in new spark plugs and coils. A few months ago we put in new camshaft and crankshaft sensors. It is getting more often that it does this when I start it up and it feels a little under powered. What could be causing it to act this way?