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It is very possible the injector is the cause of the problem. Since it is on the individual cylinder I agree with your summation of the mas or IAC being the cause. What I would do is swap the injector with the one next to it and see if the misfire code moves to that cylinder. If it does, replace the injector, if not, then I would check the wiring harness for the fuel injector, it may be hitting something at times and shorting out.
Please let me know if there is any more I can do to help you from here.
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