– carefully inspect the underhood space. Turn off the ignition and check the reliability of the fastening and seating of all wires and connectors at the ignition coil and high-voltage wires. Start the engine and listen to its operation: the crackling sound when the high-voltage current breaks down to the "ground" is weak, but distinct. In complete darkness, the spark is clearly visible when breaking down;
– replace spark plugs regardless of their condition and mileage. Pay attention to the condition of the spark plugs: if it is not in compliance with the norm, you may have to repair the engine or its systems.
A specific cause of jerking during steady movement of a Ford Focus II may be a failure of the throttle position sensor built into the throttle assembly cover.
Additional symptoms that confirm a faulty sensor include:
- uneven engine operation at idle;
– reduction of maximum engine power.
The throttle body cover is non-separable, so it cannot be repaired. If a sensor malfunction is detected (see "Checking and replacing engine management system sensors"), replace the throttle assembly with the cover.