Why does the classic Focus have unstable idle speed that fluctuates up and down?
2 Answers
Classic Focus idle speed fluctuating up and down reasons are as follows: 1. Throttle body dirt: Impurities in the air and oil sludge generated by gasoline cause the vehicle's throttle body to become dirty, changing the channel cross-section and preventing precise control of air intake. 2. Throttle body carbon deposits: Carbon buildup on the throttle body and insufficient atomized combustion from the fuel injectors. 3. Exhaust pipe blockage: Blocked exhaust pipe leads to poor exhaust flow. 4. Insufficient vacuum: Air leaks causing insufficient vacuum, 5-cylinder pressure deficiency, and severe automatic wear phenomenon. It needs to be checked and handled at a 4S shop or repair shop as soon as possible.
As someone who frequently works on cars, I often see the issue of unstable idle speed in classic Focus models, where the RPM fluctuates erratically. There are several possible causes: first, excessive carbon buildup, where the throttle body or idle air control valve is clogged with sludge, disrupting airflow; second, problems with the ignition system, such as worn spark plugs or faulty ignition coils, causing engine misfires and shaking; third, malfunctioning sensors, like the throttle position sensor providing inaccurate readings; fourth, vacuum leaks, where external air seeps in; and fifth, in rare cases, the ECM software may need an update. From my experience, leaving this issue unresolved can negatively impact fuel efficiency and, over time, cause significant engine damage. DIY checks can be challenging, so I recommend taking it to a professional shop for cleaning or part replacements—spending a little time and money now ensures safety and savings in the long run.
