2002 Accent misfire

I have had continual problems with a '02 accent. It has been misfiring since about 35K. The main problem is that the cause cannot be found. The check engine light will flash once in a blue moon (often months
apart.) I was told right around 30K (the first time I took it in for misfiring) that the plugs "must" be Hyundai brand. Since the problem continued the Autolite plugs I bought and installed at 30K were replaced AGAIN with Hyundai plugs around 45K. The wires, plugs, and coil have all been replaced (at 45K.)
Alas, the problem had continued. When the vehicle reached 55K I moved to another state. Because of my worries that the manufacturer warranty would expire before this issue was addressed I called Hyundai directly and setup a case. The car was taken to the third dealer. I was assured the problem was caused by air in the fuel line because the tank was low, and that the misfire codes in the computer were false. I was instructed to ignore it. Since that time, the problem has continued regardless whether the gas tank is full or empty (this is still happening today.)
Around 75K the car came up for another spark plug replacement. This time I made SURE to purchase Hyundai OFFICIAL plugs. I verified the gap on the plugs and made sure it was right in the middle of specs. The plugs were torqued in just as HMASERVICE showed.
After replacing the plugs the problem appears more evident (the engine light has flashed three times this month.) When the car sits overnight (must be more than 4-6 hours) and I start it, the vehicle will hesitate for about 5 seconds. The rpm's are low and the car acts as if it will stop running. After about 5 seconds the rpm's shoot up to about 1000 and the car runs FINE after that (SOMETIMES the engine light flashes while it tries to catch up.) If I let it sit for hours without starting it the problem does not show again. This issue only occurs if the car sits overnight. I have not noticed any performance issues, no loss of fuel economy, no hesitation.
So I ask you, WHAT THE *$&%(!!!
Does anyone have any idea what may be causing this problem. Also, I was wondering if I have any recourse with Hyundai now that there are 78K miles on it?
I appreciate any response to this problem.
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You indicated that you "opened a case" with Hyundai so my first question is what has Hyundai responded to you? You don't indicate whether they are working with you or not so how can anyone suggest if you have any recourse? Have you had the car scanned? Are there any codes stored? With today's cars this is always a good place to start. Though scan codes are not bullet-proof, attempting to offer advice or throwing parts at a car without considering the codes is a waste of money and time.
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-Mike-
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Perhaps an injector isn't sealing properly and if the car sits overnight there's too much fuel in that cylinder?
Contact Hyundai again and let them know what is occurring. Take it in to the local dealer and have it checked. Then cross your fingers. I'd be surprised if you get assistance, but you never know.
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