08 and below does not have VVT 09-11 does, could you have some dirty injectors? have you run some cleaner in the gas I use Beryman's B12 once in a while cheapest at Walmart and has about what all the other more expensive ones have look at the chemicals in them, when my car (08 was cold at times it would be hard to start or falter and rough idle a while in the winter time not really the cold in Arizona but could be around 45 and below 32 once in a while and that would fix it do you have a scan tool I had to buy one to check my car out was always borrowing one, I ended up getting a Bluetooth on from Autel ApMax Ap200 for around $45 shipped, when working on any FI I always verify fuel pressure first then the fuel trim.

on the 08 you can reset the ECM by disconnecting the battery or anytime the battery is disconnected it's reset, so it has to go through a relearn on idle control you have to start it up let it idle till completely up to temp put it in every gear and back to park then put on the ac and off and do it again with each gear and ac do it when the car is as cold as possible after cleaning the fuel system make sure to do it when you are going to drive the care some distance or us it when you have a low tank and drive it some than refill as those cleaners are hard on the plastic and rubber parts don't let sit in the tank a long time I'd go an a 50 mile drive