Volvo 960 severe engine shaking on start up in hot weather on Volvo 960

Some Volvo 960 owners report experiencing severe engine shaking on start-up during hot weather, which may be attributed to several factors. Worn out or faulty spark plugs are commonly cited as a cause of engine vibration. Additionally, issues with the fuel pump relay or engine coils could contribute to this problem. Some owners notice that a sharp vibration immediately after startup might indicate a missing combustion spark in one of the cylinders, although this may resolve as the engine warms up. Temperature control issues may also be at play, particularly if the cooling fan activates during initial start-up. Furthermore, the rich fuel mixture when the engine is cold can lead to misfiring as unmeasured air enters, resulting in shaking and rough running. Lastly, some owners find that replacing engine and transmission mounts can alleviate shaking issues, especially at certain speeds or during turns. A thorough inspection by a qualified mechanic is recommended to accurately diagnose the cause of the severe engine shaking.