HELP: High Idling 2002 Y61 Patrol GU ZD30 A/T

I was on my way to a meeting last night driving the Patrol. When I came to stop, I shifted the gear lever to neutral (N). To my surprise the engine suddenly revved itself to about 1,000-1,200 rpm even without me touching the throttle.

I shifted back to drive (D) and the revs got subdued a bit to a more docile 750rpm but I could still feel that the engine wanted to rev.

I let the car rest overnight and the same thing still happened on my way to work this morning. Whenever I shift to Park or Neutral, the engine would rev to 1,000-1,200 rpm.

There are no illuminated idiot lights on my dashboard.

What could be the problem? Hope you guys could help out.