Why Does the Volvo S90 Engine Shake When Cold?
2 Answers
Volvo S90 engine shaking when cold can be attributed to the following reasons: 1. Low ignition energy at low engine temperatures. When the engine temperature is insufficient, both fuel and lubricant temperatures are low, requiring more fuel injection during cold starts to meet power demands. Larger spark plug gaps result in weaker ignition energy. Poor fuel atomization at low temperatures demands higher ignition energy. Over time, spark plug gaps tend to widen, reducing ignition energy and affecting engine performance, leading to shaking. Additionally, aging ignition coils, high-voltage wires, or electrical leaks can also decrease ignition energy. 2. Incorrect engine air-fuel mixture ratio. Improper fuel-air mixture occurs in both open-loop and closed-loop control systems. In closed-loop systems, oxygen sensors require a minimum operating temperature of 370°C. If the exhaust pipe temperature doesn't reach this level upon startup, the oxygen sensor remains inactive. This causes the ECU to miscalculate, leading to errors in fuel-air mixture and ignition timing control, reducing power output and causing shaking. 3. Carbon buildup on engine valves and intake ports. Carbon deposits can absorb fuel (similar to soil absorbing water from a riverbank), causing ECU miscalculations. For instance, if the ECU injects 100 units of fuel-air mixture but only 90 units reach the cylinder (with 10 absorbed by carbon deposits), even complete combustion of the remaining 90 units won't provide sufficient power, inevitably resulting in shaking. 4. Varying cylinder conditions. After prolonged use, clearance between cylinder liners and pistons becomes uneven—some larger, some smaller. During cold starts without proper oil lubrication, cylinders with larger clearances may leak high-temperature gases, reducing power output.
My own Volvo S90 also experienced severe shaking during cold starts, likely due to aging spark plugs or ignition coil issues. At low temperatures when the engine is cold, the oil passages aren't as smooth, leading to uneven combustion and increased shaking. Additionally, carbon buildup on fuel injectors or intake valves can obstruct fuel flow and worsen the vibration. Don't underestimate oil quality - using oil with incorrect viscosity can thicken in cold weather, causing insufficient lubrication and extra vibration. I recommend checking if spark plugs need replacement and regularly using fuel additives to clean carbon deposits, as proper maintenance can prevent major issues. If shaking is accompanied by noise, it might indicate loose engine mounts - get it repaired at a professional shop immediately to avoid long-term engine damage.
