Intermittent P0300 Misfire in 2001 Mazda Protege: Diagnosis and Solutions

We are experiencing an intermittent P0300 random misfire code on our 2001 Mazda Protege 2.0L with automatic transmission. The issue is not constant — the vehicle runs smoothly for periods, then suddenly stumbles for 5 to 15 seconds before returning to normal operation. During these episodes, the Check Engine light flashes briefly and then remains steady. First occurrence: While driving on a freeway, followed by a stop at an exit ramp about 15 seconds later. The car ran fine for approximately 12.7 miles until overnight, after which we drove another 5 miles to a dealer. At the first dealership, they found P0300 and P0462 codes. They inspected spark plugs and intake gasket — both were deemed in good condition. Fuel trim was noted as being significantly high in negative value. The air flow meter was replaced due to deterioration. After clearing the codes, a road test showed no issues (cost: $337.15). Second occurrence: 715 miles later, while driving on city streets below 30 mph, we detected code P0300 using a CP9125 scanner. We visited a different local dealer who confirmed the P0300 random misfire. They recommended checking spark plugs and wires, noting that both must be present for ignition to start. All spark plugs and two plug wires were replaced, along with two boot assemblies (spark and coil). After clearing codes and completing an 8-mile road test, the vehicle ran smoothly. Third occurrence: Just 10 miles later, at a city intersection, P0300 reappeared. Codes were cleared and driving resumed. Fourth occurrence: Five miles after that, under identical city conditions, the same code returned. The car underwent a comprehensive 60,000-mile service when new and was rated as being in excellent condition at that time. The first dealer noted good maintenance history with no prior issues. Our concern lies in the intermittent nature of this misfire — it's highly unlikely that all four cylinders would simultaneously experience intermittent spark or fuel delivery failures. This raises questions about underlying mechanical, sensor, or vacuum-related causes. Given that symptoms often occur during stops at traffic lights or low-speed city driving (around 25–30 mph), changes in engine load and vacuum may be contributing factors. What could be causing this intermittent P0300? Are there known common issues with the 2001 Mazda Protege’s fuel system, EGR valve, or intake components that might trigger such behavior?