Is it normal for the idle speed to increase on its own while driving?

[Jamie]

It is normal for the idle speed to be higher during startup. Idling can easily lead to oil burning: During idling, the throttle opening is small, and the vacuum inside the intake manifold is high, which can easily draw oil vapor into the intake manifold. Some of it deposits inside the intake manifold, forming carbon-like substances or what is called coking. Prolonged low-speed driving or idling, especially in turbocharged models, may result in a pool of oil behind the throttle in the intake manifold. However, this oil usually disappears after highway driving. Idling can easily cause carbon buildup: During idling, the air-fuel mixture tends to be richer. Therefore, prolonged idling with a richer mixture can lead to carbon buildup in the engine. Similarly, stop-and-go driving at low speeds, such as frequently accelerating and braking, can also cause carbon buildup. This is because the engine alternates between enriching and reducing fuel injection, which is prone to carbon accumulation.