Causes of Intermittent Engine Shaking
4 Answers
Engine intermittent shaking may be caused by the following reasons: 1. Engine intake pipe leakage: The intake system contains numerous intake manifolds or valves. If gas leaks into other components, it may cause the air-fuel mixture concentration in the intake manifold to become excessively high or low, leading to intermittent engine shaking or weak idle performance. 2. Fuel system blockage or malfunction: Blockage in the fuel tank vent hole, fuel tank switch, fuel filter, or fuel lines between the tank and carburetor may prevent the engine from receiving the required fuel supply during idle. This results in a lean air-fuel mixture, reduced power output, and idle shaking. 3. Idle control valve malfunction: The ECU controls the opening of the idle control valve based on signals such as engine speed, temperature, and throttle position to maintain stability. If the valve malfunctions, uneven air distribution occurs, causing fluctuating idle power and vehicle shaking. 4. Engine carbon buildup issues: Carbon deposits, including cylinder carbon, throttle carbon, spark plug carbon, and intake carbon, directly affect engine power output. Excessive carbon buildup reduces ignition energy and intake efficiency, leading to unstable power output, idle shaking, and poor acceleration.
Last week my old ride had the same issue. Intermittent engine shaking is most commonly caused by ignition system problems, like spark plug leakage or aging ignition coils - just like how my car smoothed out immediately after replacing all four spark plugs. Next could be fuel system issues, such as dirty injectors or unstable fuel pump supply, causing occasional 'gasping' during acceleration. Air intake system problems like carbon buildup on throttle bodies or clogged air filters can also starve the engine. Don't overlook worn engine mounts either - that day the mechanic just touched it and said the right-side mount had collapsed. Remember after using fuel system cleaner last time, the cold-start shaking improved significantly. If it still shakes when warm, consider whether the O2 sensor readings are drifting.
Encountered this situation several times. Let me share some basic troubleshooting tips: If the tachometer needle jumps up and down at idle, it's likely due to a dirty and sticking throttle body – a simple cleaning should fix it. If the car jerks during acceleration, first check the spark plug gaps and high-tension wires. If the shaking only happens when the AC is on, the engine mounts might be completely worn out. Another easily overlooked factor is fuel quality – gasoline mixed with water can make the engine sputter like it's hiccuping. Last time I checked a neighbor's car, the issue disappeared after switching back to fuel from a reputable gas station. If the check engine light flashes, use a diagnostic tool to check for misfire records. Don't delay too long – prolonged shaking accelerates component wear.
After more than a decade in auto repair, I've summarized this pattern: A few shakes during cold starts are normal, but persistent shaking requires investigation. Start with the simplest check—has the air filter not been changed in three years? A clogged filter can cause an overly rich fuel mixture. Next, open the hood and feel the ignition coils to see if their temperatures are consistent—the one that's hotter is likely faulty. The most direct method is performing a cylinder cut-out test by pulling the spark plug wires—if pulling a wire doesn't change the shaking, that cylinder isn't working. Additionally, an overdue fuel filter can lead to insufficient fuel pressure, a common issue in older cars. Cracks in vacuum lines can also cause random shaking. If all else fails, check the crankshaft position sensor connector for oxidation or poor contact.
