What causes the unstable idle speed of the classic Focus?

[VonGia]

The reasons for the unstable idle speed of the classic Focus are as follows: Dirty throttle body: Impurities in the air and sludge from gasoline cause the throttle body to become dirty, changing the cross-sectional area of the passage and making it impossible to precisely control the air intake. Carbon buildup on the throttle: Carbon buildup on the throttle and insufficient atomized combustion from the fuel injectors result in fluctuating idle speeds. Clogged exhaust pipe: A clogged exhaust pipe leads to poor exhaust flow. Insufficient vacuum: Air leaks cause insufficient vacuum, resulting in low pressure in the 5th cylinder and severe automatic wear. It is necessary to visit a 4S shop or repair shop as soon as possible for inspection and repair.