My 2004 Hyundai Sonata cold starts great (i.e. when I first get into the car for the day, morning or afternoon). The problem I have is that when I stop the car after driving around for a while it sometimes sputters at start up. It only happens if the motor is warm, and it has been parked for a medium period of time (i.e. about an hour). Sometimes the sputtering doesn't occur immediately at start up, but when backing out of the parking spot, or I've even had it occur when pulling out of the parking lot itself. After the sputter I give it a little more throttle, and it takes off. It runs great after that. Any ideas?
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Hot-start problems are indicative of loss of pressure in the fuel line. This is usually caused by a leaky fuel injector.
The reason why this happens only for hot starts is because the fuel is more likely to vaporize as temperature increases. In order to avoid vaporization problems the fuel lines are expected to be pressurized during a hot start. Of course, if there is a fuel leak then the fuel may have partially vaporized by the time it reaches the fuel injectors, resulting in the "sputtering" symptoms that you have experienced.
The first thing that comes to mind is an ignition problem. As in, either your coilpack, HT leads (the cable running from the coilpack to the spark plug) or a spark plug is faulty. THe symptoms are consistent with what you describe.