What Causes Engine Idle Shaking After Overhaul?
2 Answers
Reasons for engine idle shaking after overhaul: 1. Engine intake pipe leakage: The intake system contains many intake manifolds or valves. Leakage in these components allows unintended gas entry, causing the air-fuel mixture concentration in the intake manifold to become too rich or too lean, ultimately leading to intermittent engine shaking or weak idle performance. 2. Fuel system blockage or malfunction: Blockages in the fuel tank vent, fuel tank switch, fuel filter, or fuel lines between the tank and carburetor prevent the engine from receiving adequate fuel supply during idle. This results in a lean mixture, weakened engine power output, and idle shaking. 3. Idle control valve failure: Most EFI engines regulate idle operation via the idle control valve. The ECU controls the valve opening based on signals such as engine speed, temperature, and throttle position to maintain stable idle. Any malfunction causes uneven air distribution, resulting in fluctuating idle power and vehicle shaking. 4. Engine carbon buildup issues: Carbon deposits in critical areas including cylinders, throttle body, spark plugs, and intake tracts directly affect engine power output. Excessive carbon buildup reduces ignition energy and intake efficiency, ultimately causing unstable power output, idle shaking, and poor acceleration.
With years of experience in car repair, I've seen many cases of rough idling after major overhauls. The most common causes are improperly tightened engine mounts or poorly adjusted ignition systems. Loose mounts can cause the entire engine to shake, especially noticeable at idle. For ignition issues, incorrect spark plug gaps or poor contact in high-voltage wires can lead to misfires and shaking. Another possibility is inaccurate calibration of the throttle position sensor, affecting idle stability. Additionally, newly replaced parts like fuel injectors or oxygen sensors with defects can also cause problems. I recommend checking step by step: first inspect if the mount bolts are loose, then test the voltage of spark plugs and ignition coils. If you can't fix it yourself, it's best to return to the repair shop and have a technician read the fault codes with a diagnostic tool. Don't delay too long, as prolonged shaking may damage other components and increase repair costs. Safety first, timely action is key.
