What causes engine idle vibration when the coolant temperature rises?
2 Answers
Idle vibration is likely caused by carbon deposits in the engine or throttle body. Below are the relevant explanations: Causes of idle vibration: When there is excessive carbon buildup inside the engine, the gasoline injected by the cold start fuel injector will be largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts and making ignition difficult. In this situation, the engine will only start easily after the carbon deposits have absorbed enough gasoline to become saturated. After starting, the gasoline adsorbed on the carbon deposits will be drawn into the combustion chamber by the engine's vacuum suction force and burned, making the air-fuel mixture overly rich. The constantly changing lean and rich air-fuel mixture causes idle vibration after a cold start. Inspection method: When the engine idle is unstable, first adjust the idle speed. If the problem persists after adjustment, check whether the idle jet and idle air jet are clogged.
I've encountered a similar situation before where the idle would shake like it couldn't catch its breath once the car warmed up. The most common cause is aging engine mount rubber, which loses its damping effect due to thermal expansion and contraction. Another issue is unstable cylinder pressure, where piston ring wear leads to noticeable high-temperature gas leakage. If the spark plugs are eroded, insufficient ignition energy when the engine is hot can also be a contributing factor. Last month, while cleaning the throttle body, I noticed that cars with severe carbon buildup show particularly obvious unstable air intake under high-temperature conditions. Also, don't overlook the fuel delivery system—clogged fuel injectors can cause fluctuations in the air-fuel mixture concentration. This problem needs to be addressed early. I once delayed repairs and ended up stalling in traffic.
