P1602 is a code that is used by different manufacturers for different purposes. There also might not be consistency within a particular manufacturer's production, especially year-to-year.

Keeping these factors in mind, according to my 2007 Subaru service manual, P1602 relates to an error in idle speed, or exhaust gas temperature, when the engine is cold.

When the engine is cold, the idle speed is set higher, and the timing altered to increase exhaust gas temperatures so that the catalytic converter will heat up quickly (the converter works effectively only when it is very hot).

The code will be set, and the CEL turned on, after the same symptom is identified in two consecutive driving cycles. The CEL will go out on its own if the fault is not detected in three consecutive driving cycles. The code will remain in memory for 40 driving cycles without the fault appearing.

If the code is the same for your 2010, it's emissions related and covered by your warranty. Probably best to take the car to the dealer.

 

So, rear o2 sensor or ECU glitch or IAC issue ... unless it's a turbo then maybe exhaust gas temp sensor ? Either way, sounds like a warranty issue to me.