IT may also be an O2 sensor malfunctioning. Those usually tend to go out around the 60,000 mile mark, earlier or later, give or take. It may not flag a CEL right away either. I had symptoms similar to what you are having and found that my heated O2 sensor was the problem. You may also want to check your charcoal canister too and see if that needs to be replaced. Those usually don't need to be replaced, but they will if your car is running rich. When you start your car up and let it warm up for a while, can you smell fuel fumes emitting fromt he car when you are standing next to it? If so, then the charcoal canister is full.