Nissan Repair: Idle question, air control valve, infinity g37s

Question
I have a 2008 Infinity G37S that normally idles around 625 RPMs.  However, I've noticed after running it hard and/or on hot days the car starts to idle at 800 RPM's for some reason.  It NEVER starts off idling at 800 when I initially turn the car on and let it warm up for a few minutes...it only starts doing it after driving it for a while.  If I turn the car off and then back on the car normally goes back to idling at 625 RPMs.  I don't recall the car doing this during the first 10 months I owned the car, but over the last couple months I have definitely noticed it.  It's a little trickier putting the car in motion when it idles at 800 RPM...I really have to give it the gas.  I don't like it!   

I've ask the Infinity dealership about this and they said it could be dirty air and/or bad gas and that there's nothing wrong with the car.  While this is not really causing a problem, I can't help but think their explanation is a load of BS.  So, my question is, do you know why it would be doing this and should I be concerned about it?

Thanks,
Steve

Answer
Steve,

Awesome car!  Drive by wire makes things interesting.  That is, your throttle is not controlled by a cable but a stepper motor in the throttle and a resistor on the gas pedal.  Normally, I would say the car has an idle air control valve that is sticking.  But, since yours does not idle properly, all the time, I would think the stepper motor is not referencing properly.  I would take the car back in and ask them to document the idle problem again.  It should not matter how the car is driven as the idle should always be consistant.  There is a service bulletin on your car for the air meter "ITB 05-051" that could be part of the problem.  The air meter monitors the air coming into the engine and if it is not working properly it could cause a similar problem to the one you describe.  Let me know what the dealer says...