How to Determine Excessive Carbon Deposits in a Car?

[LeoLee]

The formation of carbon deposits is mainly related to incomplete combustion of gasoline and frequent low-speed operation of the vehicle. Symptoms of excessive carbon deposits are as follows: 1. Engine vibration: The engine produces intermittent and rhythmic vibrations under idle conditions. 2. Unstable engine idle: The engine's speed fluctuates erratically, sometimes high and sometimes low, during idle. 3. Weak engine acceleration: When carbon deposits accumulate severely, the engine may exhibit weak or sluggish acceleration, accompanied by abnormal vibrations and increased fuel consumption. 4. Engine knocking: Excessive carbon deposits in the combustion chamber can increase the engine's compression ratio, potentially causing premature combustion of the air-fuel mixture and resulting in knocking. 5. Cylinder scoring: If carbon deposits accumulate near the piston rings or if deposits from the cylinder head or valves fall onto the piston rings, it can lead to cylinder scoring. In severe cases, it may even cause "seizure" of the cylinder.

[VincentLee]

Having driven for over a decade, I've identified several clear signs of carbon buildup. Cold starts are particularly difficult, sometimes requiring two turns of the key to get the engine going, with the starter motor sounding noticeably strained. At idle while waiting at traffic lights, the entire car shakes like a phone on vibrate mode, especially noticeable through the steering wheel, and sometimes the tachometer needle jumps up and down. The most frustrating part is during acceleration – you press the gas pedal but the engine just roars without delivering power, making overtaking particularly unconfident. Fuel consumption has also quietly increased; where a full tank used to last 500 kilometers, now the low fuel light comes on after just over 400. The exhaust smell has become pungent too, especially noticeable when using the air conditioning in recirculation mode. When all these symptoms appear together, there's about an 80% chance it's time to clean the throttle body and fuel injectors.

[NolanMarie]

Let me explain from a maintenance perspective. Carbon deposit issues can actually be detected early. The most obvious sign is difficulty starting the engine, especially during the first ignition after leaving the car overnight - you'll clearly feel it takes one or two seconds longer than when the car was new. Unstable idling manifests as RPM fluctuations; normally it should stay steady around 800 RPM, but with significant carbon buildup it may drop to 600 RPM then suddenly jump to 1000 RPM. Sluggish acceleration shows as delayed response when pressing the accelerator, with particularly noticeable power loss when climbing hills with AC on. Increased fuel consumption usually appears last - be alert if you suddenly notice 1-2 liters more per 100 kilometers. Also pay attention to changes in engine sound; slight knocking noises (ticking sounds) may originate from carbon deposits in the combustion chamber. Regularly checking the air filter condition can also provide indirect clues, as a dirty filter accelerates carbon buildup.

[AmyLynn]

As a driver who has owned seven or eight cars, you can judge carbon buildup by checking three things. Difficulty starting is the most common sign, especially when the ignition time becomes noticeably longer on cold winter mornings. Idle shaking feels like a phone vibrating, with the tachometer needle fluctuating by more than 200 RPM. Throttle response lags during acceleration, particularly when the RPM reaches 3000 and the power fails to connect. It’s most noticeable on the highway—where you used to hit 120 km/h effortlessly, now you have to press the accelerator harder. Occasionally, the check engine light may come on, with a code indicating a rich air-fuel mixture. If you touch the tailpipe and find a lot of black soot, that’s also a sign of incomplete combustion. Address these issues promptly to prevent the carbon deposits from hardening and becoming harder to clean.