It's hard to diagnose a miss without being there to see it in person, but here goes- The miss could be the result of many things, e.g. a vaccum leak, a leaking or plugged fuel injector, a defective ignition coil, sparkplug connector short, worn sparkpugs, poor valve sealing ect... Start with a scan of the ECM. Are there any DTC's present? DTC #300 indicates a random miss, #301 through 308 idicate the exact cylinder that is malfunctioning. Do some basic underhood checks and report back what you find .... we'll help you figure out from there.