Engine revs drop initially when pressing the accelerator

[rossh123]

Hi All,

I have a 1999 Yaris 1.0L. When the engine is fully warmed up the idle drops to around 500-600 RPM, which is supposed to be normal for the Yaris.

However, when pressing the accelerator to pull away the engine will almost stall before the revs come up to where they should be. This is particularly bad when needing to pull away quickly because the car won't go for a second or two because the idle drops before rising back again. This doesn't happen when the engine is cold because the idle speed is higher. I hope this makes sense.

I've also tried blipping the accelerator in neutral, and it does exactly the same thing.

Can anyone help as to what this may be?

[GreenV8S]

A faulty throttle position sensor would cause symptoms like that on some cars - don't know whether it applies to yours.