Why does the car idle unstable when the air conditioner is on?
3 Answers
The reasons for unstable idling when the car air conditioner is on: 1. There is a fault in the air conditioning system, which may be caused by a malfunction in the air conditioning circuit or intermittent operation of the air conditioner; 2. There is a problem with the engine, the most common being excessive carbon deposits in the engine. The car air conditioner refers to the air conditioning device installed in the car, which can cool, heat, ventilate and purify the air in the compartment. Carbon deposits in the engine are the main cause of car shaking. When there is too much carbon deposit inside the engine, the gasoline sprayed by the cold start injector will be largely absorbed by the carbon deposits, resulting in a too lean mixture during startup, which can cause sudden stalling. The solution is to clean the fuel system, check the idle speed motor, and clean the throttle. Spark plugs are consumable parts and need to be replaced regularly. If it is found that the spark plugs have excessive carbon deposits or the ignition gap is too large, they need to be replaced.
As someone who's been working around cars for a long time, I feel that unstable idling when the AC is on is mostly due to increased pressure in the engine system. Once the AC compressor kicks in, it draws a significant amount of power from the engine. The idle speed is already quite low, and when the load suddenly increases, if the idle control valve responds slowly or gets stuck, the RPM will fluctuate back and forth, which can be quite unsettling. This is especially true for older cars where a clogged air filter worsens the situation by restricting air intake. I've seen many cases where carbon buildup blocks the throttle passage, causing poor airflow and uneven air-fuel mixture after turning on the AC, leading to engine shuddering. I recommend checking the air filter first and replacing it if it's dirty. If the idle is still unstable, quickly take it to a repair shop to read the ECU data with professional equipment to identify the specific issue. Don't delay too long, as unresolved problems like this can affect overall driving stability. It could be dangerous if the engine stalls on the highway.
I'm used to the electronic control systems in vehicles, and unstable idle speed when the AC is on is often caused by the control unit. The ECU needs to monitor and adjust the idle air control valve or throttle opening in real-time to compensate for the additional load from the AC. However, if sensors like the throttle position sensor fail and provide inaccurate signals, the ECU will make incorrect adjustments, causing the RPM to fluctuate wildly. Loose wiring connections or faulty relays are also common culprits, leading to interrupted control signals. Additionally, issues with the mass airflow sensor can cause deviations in air calculation, directly affecting fuel injection. It's best to use a diagnostic tool to scan the onboard system for trouble codes and pinpoint the problem for repair. Don’t underestimate these fluctuations—over time, the ECU might fail completely, and repair costs will skyrocket.
