What Causes the Car to Shake After Starting?
3 Answers
There are three main reasons why a car shakes after starting: 1. Low ignition energy: The first issue a car faces during a cold start is low temperature. The engine's internal temperature is insufficient, and both fuel and lubricant temperatures are low. Therefore, more fuel needs to be injected during a cold start to meet power requirements. The larger the spark plug gap, the lower the ignition energy. Poor fuel atomization at low temperatures requires higher ignition energy. Over time, the spark plug's ignition gap tends to widen, reducing ignition energy and affecting performance, causing the car to shake. 2. Carbon buildup on valves and intake passages: If carbon accumulates on the engine's valves and intake passages, it absorbs some fuel, leading to ECU miscalculations. For example, if the ECU controls the injection of 100 units of air-fuel mixture but only 90 units enter the cylinder, even complete combustion of these 90 units won't achieve the required power, resulting in shaking. 3. Incorrect air-fuel ratio: Inaccurate air-fuel mixture ratios can occur in both open-loop and closed-loop control systems. In closed-loop control vehicles, the oxygen sensor's minimum operating temperature is 370°C. If the exhaust pipe temperature doesn't reach 370°C upon starting, the oxygen sensor won't function. This causes the ECU to make errors in controlling the air-fuel mixture and ignition timing, reducing the car's power output and causing shaking.
The car shakes and jerks after starting, which is heartbreaking to watch. The possible causes are varied, such as aging or dirty spark plugs, which fail to ignite properly, causing the engine to misfire. Another possibility is clogged fuel injectors, preventing fuel from entering the cylinders and resulting in uneven engine operation. Loose engine mounts are also a common issue—when the rubber deteriorates or bolts loosen, the engine vibrates excessively. Over the years running my auto repair shop, I’ve seen many cases where excessive carbon buildup in the throttle body disrupts air intake, leading to unstable computer control, or where poor-quality fuel with impurities affects combustion. Sometimes, unstable battery voltage is the culprit, causing fluctuations in power after startup that lead to shaking. Remember not to delay—first check easily replaceable parts like spark plugs and mounts. Otherwise, prolonged shaking can damage the engine, making repairs even costlier.
The car starts shaking right after ignition, which is something to be careful about. Having been a car owner for many years, the most common issue is fuel system problems, such as clogged fuel injectors or insufficient fuel pump pressure, causing the engine to struggle. A dirty mass air flow sensor can also send incorrect data, making the computer unable to stabilize the air-fuel ratio. Other possibilities include faulty ignition coils failing to produce sparks, or uneven cylinder compression due to severe piston wear in older cars. Once shaking occurs, avoid long-distance driving—it's unsafe and can distract you, leading to accidents. Last month, I experienced this and fixed it by replacing a spark plug. It's recommended to first use an OBD scanner to read the trouble codes before deciding what to repair, saving unnecessary trips to the mechanic.
