Why does the Focus shake at idle when the air conditioning is on?

[McLondyn]

The reasons for the Focus shaking at idle when the air conditioning is on are as follows: 1. Severe engine carbon deposits: Engine carbon deposits are the main cause of car shaking. When there is excessive carbon buildup inside the engine, the gasoline sprayed by the fuel injector during a cold start is largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts, which can easily cause shaking. 2. Ignition system failure: Excessive carbon deposits on the spark plugs or an overly large ignition gap can lead to ignition failure. 3. Oil pressure issues: Abnormal fuel pump supply pressure or incorrect readings from the intake pressure sensor can cause poor fuel pump performance, leading to body shaking.