What is the problem when the car body shakes at idle speed without any fault code?

[McLillian]

Reasons for car body shaking at idle speed without fault codes: 1. Severe burning of the distributor cap contacts: If the contacts of the ignition system's distributor cap are severely burned, it will cause spark jumping, mostly occurring between the corresponding posts on the cap, resulting in severe idle speed fluctuations and significant power loss. 2. Faulty ignition coil: This can also lead to cylinder misfire, and often it is the ignition coil problem that causes severe burning of the distributor cap. After the ignition coil fails, it is also most likely to cause severe power loss and sudden engine stalling. 3. Cylinder wire wear: This can also cause engine misfire. To check whether the cylinder wire is working properly, simply pull out the cylinder wire, plug it into the spark plug, and start the engine to observe. 4. Ignition system problem: Sometimes, ignition system issues can also cause the electrode discharge part of the spark plug to become rounded due to burning after working for a period, making the spark jump position not in the spark plug gap or the spark plug not firing at all, which directly leads to the cylinder not working.