Why does the car shake when stationary in P and N gears?
2 Answers
When the engine is idling in D and N gears, if the engine idle vibration exceeds the expected value of ±20r/min, it is not normal. The following are specific explanations: 1. Intake system: The air flow meter or its circuit is damaged, the engine control unit plug has poor contact or the internal computer is damaged, the throttle motor is damaged or stuck, the idle stepper motor, duty cycle solenoid valve, or rotary solenoid valve is damaged or stuck. 2. Fuel system: The injector is clogged, has poor sealing, or sprays fuel in a line, the fuel filter is clogged, the fuel pump filter screen is clogged, the fuel pump has insufficient pressure, the fuel pump safety valve spring has too little tension, or the fuel inlet pipe is clogged. 3. Ignition system: The ignition trigger signal is missing, the ignition module is damaged, the ignition module power supply or ground wire connection is loose or has poor contact, or the primary coil or secondary coil is damaged.
I've encountered this situation quite often in my car repair work. Engine vibration at idle in P or N gear can be caused by several common issues. The most frequent cause is aging and cracking of engine mounts - those rubber blocks are designed to absorb vibrations, but when they deteriorate, the shaking gets transmitted to the car body. Another common reason is misfiring due to air-fuel ratio imbalance, which could be caused by severely worn spark plug electrodes or cracked ignition coils making a cylinder intermittently misfire. Carbon buildup is also worth checking - if the black sludge around the throttle valve edge exceeds 2mm thickness, it can affect intake precision. For automatic transmissions, old and deteriorated hydraulic fluid that hasn't been changed for years can cause valve body clogging leading to jerking movements. I once repaired an old Camry that shook so badly at red lights that phones would dance in the cup holders - replacing all engine mounts immediately solved the problem. A good diagnostic tip: if gently pressing the accelerator in N gear reduces the vibration, it likely points to ignition or fuel system issues. New cars might have slight vibrations during break-in periods, but persistent shaking warrants inspection.
