My 2009 Malibu (LT, 2.4L v4, 140k miles) is having acceleration issues. It doesn't happen every time, but when accelerating from a stop the engine will run up to around 2300rpm then hang there for several seconds but then continue to operate normally. I'm not having this issue after a cold startup or when trying to change speeds. It tends to be happening when the car sits at a stop for a little while (like waiting for a light to change, or traffic to open up), but I haven't nailed down the pattern yet. No issues with shifting as far as I can tell (unless it is failing to shift to 2nd while it is hesitating).
The car is not well taken care of. It gets its regular oil changes, but other preventative maintenance hasn't been preformed in a while. During the past few years, the ECU has been throwing a bad cat converter code. I have not been able to save up the money to take it in to get it replaced since the rest of the exhaust is rusting out as well. However, it has ran fine otherwise.
I at first suspected a brake not letting go, as one of the wheels is making a speed dependent sound, but that doesn't explain why engine won't rev up.