I have a 2014 Chevy Impala - 2.5L. For past two weeks while driving I will feel a small power loss, then stabilitrak light turns on, shortly after the check engine light. When I stop at the stop light it will idle rough like it wants to turn off, but it doesn't. Then about 5 to 10 minutes later both lights turn off and the car goes back to normal. This does not happen every day. I took it to a dealer and they said it was the engine valves that need replaced. Its that true?