Recently acquired 02 Protege LX from original owner, just over 130K which had been sitting for past 5yrs non-op, since owner purchased newer truck (supposedly). At time of purchase, no noticeable issues present with car only idling & had connected my OBD2 Bluetooth adapter with Torque Pro app. No pending or stored faults were present, so assumed any abnormalities in performance would be resolved after bringing vehicle's maintenance up-to-date. Usually, not a deal breaker, and considering length of time being parked I didn't think it a major issue. However, after getting it home and realizing the performance issues wasn't just from bad fuel & dirty plugs. I've spent the past week trying to diagnose a P0300 DTC, following the On-Board Diagnostic procedures from Mazda's Workshop Manual. I've ran nearly every step with exception to compression & fuel pressures, the tester I ordered did not specify a specific fuel system. While checking continuity of the ignition system, I found 2 out of specs readings: 1st from the High-Tension Lead #1 which was just under spec @ 5.41 kilohms, and already replaced the leads, coil packs & plugs.
2nd from the ignition coil resistance, which I could not seem to get reading from either old or new packs. Specs show above 10 megohms.
If anyone can provide some clarification or insight on these 2 readings, it'll be a big help since getting to point where I'm not sure where to go from here. Thanks guys!

*UPDATE* - Plug wires were barely week old, so I took them back & got them exchanged. I had got fuel system tester loaner tool, but was missing accessories so didnt get to run pressure tests. Finished up continuity checks of components, only other below specs reading found was Air Temp Sensor. Took it out for test drive & made it back with no faults, but still has slight issue accelerating & died once while sitting at light.