What Causes the Engine to Chug at Idle?
2 Answers
The reasons for the engine chugging sound include: 1. Poor sealing: When individual engine valves have poor sealing or are burnt, severe leakage occurs in some valves, some valves have excessively small or no clearance, carbon deposits accumulate between the valve seat and valve, or the vacuum tube of some power-assisted vehicles falls off, the engine will shake at idle and produce a "chugging" sound. This sound disappears when the engine speed is increased, and the operation becomes smooth. 2. Engine issues: When the engine's air-fuel mixture is too rich, the ignition system misfires, the distributor cam is severely worn, some distributor holes are dirty, some high-voltage wires leak electricity, or some spark plugs leak electricity severely or have too small gaps. Mechanical issues such as engine misfire, some water jackets communicating with the cylinder, some intake valves getting water, piston rings not sealing tightly, rings aligning and seizing, piston tops coming off, intake valve clearance being too large, valve springs breaking, lock pieces falling off, or adjustment screws coming loose can cause the engine to produce rhythmic chugging sounds at various speeds, accompanied by severe engine shaking and difficulty in acceleration. 3. Ignition system misfire: When the distributor breaker contacts of the engine are too soft, the contact rivets are loose, the fixed bracket is loose, the valve clearance is too large or too small, or the capacitor is faulty or poorly connected, the engine will run well at low speeds but produce irregular chugging sounds at medium speeds, and the vehicle will exhibit poor driving performance.
Having worked in an auto repair shop for many years, I've encountered numerous cases of rough idling. The most common issue is ignition system failure, where spark plugs with excessive gap or electrode erosion cause unstable ignition, leading to a cylinder misfire. Aging high-voltage wires that leak electricity can also weaken the spark. Additionally, clogged fuel injectors or severe carbon buildup, resulting in uneven fuel spray, can cause engine shaking. Worn-out engine mount rubber that fails to stabilize the engine makes vibrations more noticeable. In such cases, I recommend first checking the condition of the spark plugs for any obvious damage. If you're not confident in handling it yourself, drive to a repair shop immediately. They can use a diagnostic scanner to read trouble codes and pinpoint the issue. Avoid driving with the problem for too long, as it can damage the catalytic converter.
