HELP: Code P0300 Need Expert Advice

Hope someone can help me out here. My car just registered a code P0300 which my scan tool registered: "Random Multiple Cylinder Misfire Detected"
The car had done this before about 2 months back then stopped doing it. What it did was like stutter when I start the car. Sometimes the problem would last a while then dissapear for a long time but it happened again today. And this is after the car had already been driven about 12 over miles so engine was still quite warm. Just went into Costco bought a few items and about half an hour tried starting my car and in idle mode it kinda stuttered or sputtered but the engine did not die out though it sure seemed like it was going to. Now before I take it to the mechanic I would like to know what you guys think. The car is a 96' V6 3.8LT Automatic. Last tune up was done around May of 2003 and I had the plugs and filters changed. Even had an Induction Service done. Can it be time for another Tune Up or what else could be the problem. I just don't want to get burned by the mechanic.
Thank you for any response. Winston
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What it sounds like to me:
Is a hot soak problem, where excess fuel is in the intake manifold when you are going to start it up. The fuel pressure regulator diafram being ruptured or a leaking injector would be a good place to start looking.
It's an easy test also, put on a fuel pressure gauge, cycle on the key a few times. With a 15 second rest between cycles, to pressurize the fuel system to the maximum.
Any leakage of more than one or two pounds in an hour or two. You found the problem!
Refinish king
PS
This is a seat of the pants diagnosis: Do not rip off a technician's head like this is a gospel diagnosis!

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It's not time for a tune up but you have to ckeck the computer and the mechanic can tell more my car did the same and I had to take it in it had to do with the computer when a code comes up the computer does not forget it so take it in and then they can tell you exactly what it was mine was just a broken plug wire. But you can check the wires and the plugs but I would take it in.
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