help: irratic idle

Hi folks,
can you help?
I was driving to work the other day when all of a sudden the engine management light & ESP light came on and had no throttle response. I stopped the car & turned ignition off & back on. The management light went out & throttle response came back but the ESP light has stayed on.
I have now noticed that if you rev the car in neutral and then let it idle, the revs dip to around 450rpm then settle at 850rpm. Apart from that the car seems to be driving as normal.
Can anyone shed any light on this problem.

Cheers
Rusty
 
Need a new MAF, 85 big ones from the stealers.