The P0301 code in your 2017 Toyota Camry indicates that cylinder 1 is misfiring, and the cold-start timing suggests temperature-related factors are involved. Cold start misfires often have different root causes than warm-running misfires, pointing toward components that are more sensitive when the engine is cold.
Why Cold Starts Are Different
During cold starts, the engine runs on an enriched fuel mixture, oil is thicker, and clearances are at their minimum. Components like ignition coils, spark plugs, and injectors work differently when cold. A marginal component that works when warm may fail when cold because it hasn't reached optimal operating conditions.
Cylinder 1 Specific Causes
The ignition coil for cylinder 1 may have internal degradation that only manifests when cold. The cylinder 1 spark plug may have increased resistance or fouling visible only during cold operation. Fuel injector performance can vary with temperature. Valve seal or guide wear on cylinder 1 allows oil seepage overnight that fouls the plug.
Common Cold-Start Misfire Causes
Worn valve seals allow oil to drain onto spark plugs overnight. A weak ignition coil that can't fire reliably when cold. Fuel injectors with slower response when cold. Excessive carbon on intake valves affecting cold airflow patterns. Low compression in one cylinder that's masked when warm but evident when cold.
Diagnostic Steps
Record freeze frame data to confirm the misfire occurs at cold temperatures. Inspect cylinder 1 spark plug for oil contamination or carbon buildup. Swap the cylinder 1 ignition coil with another cylinder and see if the misfire follows. Check compression on all cylinders cold and warm. Consider borescope inspection of cylinder 1 intake valve.