Gas, Premium or Regular
 

I have a 2009 2LT 2.4 engine. I read in the owners manual that I am supposed to use Premium (high octane) fuel. Can I use lower or mid-grade (less expensive) fuel without messing things up?

yes

Wow, that's short but sweet.

Yes, you can use regular unleaded without harming the engine but your performance will suffer. I find using Premium unleaded adds performance and lets the engine do what it does best without holding back for "pre ignition" issues. I also have found and documented better mileage with premium in my '08 2LT so it acually cost less to buy the high priced fuels in the long run. I have an active log book in the glove box of every gallon of fuel purchased since I bought the car new in Oct 2007, now with 49K miles.

will you notice a difference with 93 octane on the 2.2L? i havent filled up yet since i just got it 2 days ago, and who knows what the dealer filled it up with before giving it to me.

You can use reg, mid, or premium fuel. I personally have noticed better power and fuel economy with premium (we have 93 here).

2.2..... Probably not. 2.4, Yes.

I recently tried 93 in my 2.2, it did improve fuel economy, but not by much, maybe 5%. So it doesnt really pay off when the premium fuel costs 10% more. I would do it for long trips though, as a tank would go farther.
Though I wonder how long it take the engine to learn its running on different octane.

In my experience you'll see a noticeable difference in warmer temps, long drives and running your ac. I alternate every other tank in the winter and go premium only in the summer.

ran regular since I bought it. I have thought about trying premium, just to see if i can see what people are saying. But it runs fine on regular.