What Causes the Ford Focus to Shake Intermittently at Idle?
2 Answers
Ford Focus shaking at idle can be attributed to the following reasons: Ignition System Malfunction: After a certain period of operation, components such as spark plugs, high-voltage wires, and ignition coils may lead to poor performance in the ignition system. Aging Engine Components: Activating the electrical system while the engine is idling increases the engine's load, causing it to automatically raise the RPM. Unstable Oil Pressure: Abnormal fuel pump supply pressure or incorrect readings and poor performance from the intake pressure sensor. Severe Engine Carbon Buildup: The most common cause of car shaking is a dirty throttle body or excessive carbon deposits in the fuel injectors. When there is too much carbon buildup inside the engine, the gasoline sprayed by the cold start injector is largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts and making it difficult to start.
My Focus also had idling vibration issues before, and after a lot of troubleshooting, I found it was caused by several common reasons. Carbon buildup in the throttle body and fuel injectors is the most common culprit—it leads to uneven air-fuel mixture, making the engine shake erratically. Worn spark plugs or faulty ignition coils can also cause this. My neighbor’s car had a cracked ignition coil, causing a misfire that made it shake like a tractor at low speeds. Another easily overlooked issue is worn engine mounts—if those rubber blocks fail, they can’t dampen vibrations, and you’ll feel rhythmic shaking in the steering wheel. Oh, and using low-quality gasoline, clogged fuel lines, or unstable fuel pump pressure can also trigger vibrations. I’d suggest scanning for trouble codes first and checking the data stream, then focus on these three areas.
