2000 Rover 25 engine hunts, backfires and no revvs!

Hi All,

This is what I have done so far.

Temp coolant sensor = Replaced
Coil Packs = Replaced
HT Leads = Replaced
Spark plugs = Replaced

Car drives 200 Yrds either when cold or has been standing for more then about 40 mins then decides that:-

1) If your in motion that it "looses"power, IE it seems to labour

or

2) If at idle, the engine seems to hunt (revs up and down) -- not by much, but when you give light throttle its laboured.

Now, here's the thing, When it heppens at idle and the bonnet is up, a the inlet manifold (or its gubbins) makes a different sound a very bizzarre sound as a matter by fact. It could be due to the problem that this noise happens or it could be the cause? I have no idea.

The temporary cure:-

Give hard gas... Its all comes right....

So, my question is, what on earth could be causeing this problem???
What else can I do?

This is the wifes car and it makes me nervous to drive it. She showed me about the throttle hard down for a sec to make it go better.

Many thanks Rover Gurus!