My 16 versa just started this weird thing where when it's cold (below 32) and the car is started, it idles up to about 1800 rpm then drops like it's going to stall. Then it corrects itself. After it warms up the idle goes up to 750 down the 700 then back over and over, feels like a small shudder. Car only has 12k miles. Any one else experience this or know if it's normal? Driving is ok and haven't seen any issues there.