When your 2016 Ford Fiesta sets a P0302 code with noticeable vibration at idle, cylinder 2 isn't producing its normal power contribution. The Fiesta's small four-cylinder engines—1.0L EcoBoost three-cylinder or 1.6L four-cylinder—are sensitive to single-cylinder misfires that create significant vibration.
Why Misfires Cause Vibration
In a small four-cylinder engine, each cylinder contributes 25% of the engine's power pulses. When cylinder 2 misses, that quarter of the power is absent, creating a pronounced imbalance. The three-cylinder EcoBoost is even more sensitive—each cylinder accounts for 33% of power. At idle where RPM is low and there's no vehicle motion to mask it, the vibration is easily felt.
Common Causes
Ignition system failures are most common: the coil-on-plug ignition coil for cylinder 2 may have failed, or the spark plug is worn beyond service life. Fuel injector problems—clogged or electrically failed—prevent proper fuel delivery to cylinder 2. Vacuum leaks specifically at the cylinder 2 intake runner create lean conditions. Low compression from mechanical wear causes consistent misfire.
Diagnostic Process
The standard swap test identifies ignition-related failures efficiently. Move the cylinder 2 ignition coil to an adjacent cylinder. Clear codes and idle the engine. If the misfire moves to the new cylinder, the coil is faulty—a simple, inexpensive repair. If the misfire stays at cylinder 2, swap the spark plug next. Test the fuel injector if ignition components check out.
Fiesta-Specific Considerations
The 1.0L EcoBoost three-cylinder is extremely sensitive to any misfire due to its design—even a minor misfire creates significant vibration. The 1.6L naturally-aspirated engine is more conventional in misfire behavior. Either engine's direct injection system can develop carbon buildup on intake valves, affecting combustion consistency.
Repair Costs
Ignition coil replacement costs $80-$150 per coil. Spark plug replacement for all cylinders runs $100-$180. Fuel injector replacement costs $150-$300 per injector. If carbon buildup is severe, intake cleaning runs $300-$500. These compact engines are generally accessible, keeping labor costs reasonable.