P0301 Misfire Diagnosis on 1997 Geo Metro with 1.3L Engine - No Visible Misfires, Code Persists After Timing Adjustment

I own a 1997 Geo Metro with a 1.3L engine that has recently developed a P0301 misfire code. The vehicle runs smoothly under all conditions—no rough idle, no visible misfires during operation, and no smoke or performance issues in the tailpipe. When the check engine light blinks (indicating a misfire), it only occurs when the power brake is applied; otherwise, the light remains off. I have already replaced the spark plugs, ignition wires, distributor cap, rotor, and rear oxygen sensor. No vacuum leaks or EGR system issues were found during inspection. When I advance the ignition timing to its maximum setting, the P0301 code disappears and is replaced by a P0304 code (indicating misfire on cylinder 4). However, if I return to standard timing, the P0301 code returns immediately. Previously, this vehicle only had P0113 and P0136 codes, both of which have been successfully resolved. The P0301 code appeared during a road test and has not cleared since. I’ve tested the engine with no load or full load—performance remains consistent. An interesting observation: when I shut down the engine while the light is blinking and restart it, the check engine light blinks briefly at idle before stopping after about 15 seconds. This suggests a transient detection rather than an actual misfire. I am now considering whether the issue lies with the distributor or camshaft position sensor (part of the distributor assembly), as the PCM appears to be detecting a misfire based on timing relationships between the crank and cam sensors. I have already replaced the crankshaft position sensor and inspected the trigger wheel for damage—no issues found. Could the camshaft sensor be faulty? Given that advancing timing shifts the code from P0301 to P0304, I suspect a timing-related or sensor-based issue. I plan to replace the distributor with a known-good used unit soon and will also verify spark plug gaps using OEM specifications to rule out intermittent spark issues. Any insights or suggestions on diagnosing this persistent P0301 code would be greatly appreciated.