3.9 V8 revs high on start up?

Hello all
I wonder if anyone can offer any idea to a problem I'm having please
I've got a problem with a 3.9 Disco, it was running and starting fine but now suddenly on turning the key as soon as it fires it revs hard, it would go to the rev limiter if I didn't switch it off quick.
Obvious things like throttle cable and flap are free / not sticking and returning to closed position on the spring, no obvious vacuum pipes off that I can see
I have just been working on the inner wheel arch's so have moved a few minor bits like the washer bottle / air filter left side and vacuum chamber on the drivers side, just put everything back and now this revving like mad.
I assumed the obvious that I must have moved / forgotten a elec plug or vacuum hose but I've been around everything and at a loss so wonder if it could be something unrelated like the stepper sticking with the cold?
Any suggestions gratefully received

Thanks

Disco 1 or 2?

Peter

If it is stuck stepper it might rev to about 2k. I can't see how it could go higher if the throttle butterfly is closing properly.
If you suspect stuck stepper I think I would be inclined to suggest you take off and clean the plenum and ram housing, while you're about it, check the throttle potentiometer.

Well the idle is controlled from the ECU from info freceived from various sensors such as a temperature sensor, so check everything is plug in. Usually any vacuum pipe that's removed would give lumpy runing and even stop the engine.
As for vacuum chamber do you mean the round item that's collecting fuel emissions just after the fuse box and has a pipe over to the plenum.

Hello
Thanks for the replies, The stepper is just the only thing I could think of at the time but yes as your suggestion I will have to try removing the plenum etc next and see what it looks like inside/clean etc.
Yes sorry by vacuum chamber I meant the fuel emissions collector, I did not disconnect it anyway just un-clipped it and moved it to one side out of the way. It does not seem lumpy/rough running just the revving issue.
Could it be related to the cruse control? again just a thought
Thanks

The exact function and how it works in in the RAVE workshop manual, but as there's an electrical connection from the ECU, but if I remember correctly the ecu opens the valve on starting and that it.
I would isolate the isle control valve electrically first to see what happens also have a look in RAVE to see if anything is mentioned, I would think an issue like yours would be, in a flow chart for testing maybe.