Rough idle, misfiring

I have a 1996 Nissam Maxima GLE with 140,000 miles. When the car is cold, it starts right up and runs and idles fine. Once it reaches normal operating temperature it begins to idle rough, like it is misfiring or something, and it also does it during both acceleration and while driving at speed. It seems to be the worst while idleing, and like I said it only does it at normal operating temperature.
Also at the same temperature it has a little trouble starting, sometimes I have to hit the gas pedal once or twice.I have no idea when the last tune-up was done because I just purchased the vehicle. Please help!