Ford Focus ST Mk4

All direct-injection EcoBoost engines accumulate carbon on the back of the intake valves because fuel is sprayed directly into the cylinder rather than washing over the valves. Symptoms include gradual power loss, rougher idle, and increased fuel consumption. This becomes noticeable typically between 60,000 and 100,000 km depending on driving style. Short trips and gentle driving accelerate buildup. The standard fix is walnut blasting, which costs €350-500 at a specialist. Some shops charge up to €600 including intake manifold cleaning. This is not a defect but a maintenance reality of direct injection. Occasional spirited driving and using quality fuel with good detergent additives helps slow the process.

The turbocharger wastegate can develop a rattle from worn bushings or the flap sticking from carbon buildup. This is more common on cars driven gently or only for short trips, as the wastegate does not cycle through its full range. Symptoms include a metallic rattle at idle (often called the death rattle), followed by potential underboost (P0299) or overboost (P0234) fault codes, loss of power, and limp mode. Ford does not sell the wastegate actuator separately. A specialist can rebuild or replace just the actuator for €500-600, but if the turbo internals are damaged from prolonged overboosting, a full turbo replacement costs €1,200-1,600 including labour. Regular spirited driving that exercises the wastegate and using quality oil helps prevent this issue.

This is one of the most discussed issues on Focus ST forums. The wheel arch edges are painted but lack adequate stone chip protection. Water from the roof channels down past the rear lights and gets trapped behind the arch liners, rubbing away the factory paint. The rear arches are worst affected because of this water routing, though all four arches can develop rust. Many owners report visible bubbling paint within 3-5 years, even on garage-kept cars in moderate climates. Repair costs approximately €400-500 per arch for proper rust removal, treatment, and repainting. Some owners apply underbody sealant or bed liner as a more durable preventive measure. Ford's 12-year anti-perforation warranty theoretically covers this, but many owners report Ford claiming it is surface corrosion rather than perforation, which makes warranty claims difficult.

The Focus ST's stiffer suspension setup and wider tires put more stress on bushings and anti-roll bar links than the standard Focus. Anti-roll bar drop links are the most common failure, causing clunking over bumps and typically needing replacement between 40,000 and 80,000 km. These cost €150-250 per pair including fitting. Lower control arm rear bushings can also wear, causing vague steering feel and uneven tire wear. Replacing both sides with labour costs €400-700 at an independent shop. Cars driven on rough roads or used for track days wear these components faster.

Multiple owners on forums report persistent rattling from door trim, dashboard panels, and occasionally the B&O sound system speakers. This is more of a quality annoyance than a mechanical issue. The rattles tend to appear within the first 1-2 years and can be intermittent, making them difficult to diagnose at a dealer. Some Ford dealers have applied sound-deadening foam to window regulators and trim clips under warranty. On out-of-warranty cars, a trim specialist can address most rattles for €100-300. The 2022 facelift did not significantly improve this, and some owners of later cars report the same issues.

Pre-facelift cars (2019-2021) use SYNC 3, which is generally stable but can freeze occasionally, typically resolved by a key-cycle reboot. The 2022+ facelift models with SYNC 4 have more frequent issues: screen freezing during Android Auto use, black screens requiring hard resets, corrupted displays showing checkered patterns, and Bluetooth audio static. Most SYNC 4 issues can be resolved with software updates, which Ford has released multiple times. If the APIM (Accessory Protocol Interface Module) hardware fails, replacement costs approximately €600-800 including programming. Check that the latest software version is installed before purchase.