If you use the autopilot before or during your approach, make sure you turn off the auto throttle ("speed" button) when you disengage the autopilot. I've had similar situations where I disengaged the autopilot, but the engines were still going strong because I didn't click the speed button to turn it off too.
I'm not sure if I'm doing that correctly, but when I disengage the autopilot (usually when given the final vectors to intercept ILS or to visually find the runway), I go across and click the autopilot, heading, altitude, and speed buttons to turn them all off.
Dan Wolf
Cat IV
WWA1653