Hi Laurence (and Mike),
I’ve just joined the “club” so I having a look around and have noticed your question. You don’t mention which engine you have but it may not matter. From your description, I’m guessing that you have flat spot in the throttle response just as you press the accelerator.
My 3.6 had this problem and I eventually pinned the fault down to the throttle potentiometer – I took it apart to investigate and saw that the tracking inside was completely worn out just on and after the idle position, meaning that you need a bigger application of throttle to get the throttle signal. There are two pick ups which sit on the tracks – where the tracking is worn out, then there is no signal continuity from the pot.
Renewing the potentiometer completely cured the problem – its a bit of a fiddle adjusting the new one but quite straight forward (as usual, getting underneath the car is probably the biggest problem!).
On this topic, I came across one web site where the chap repaired the tracking by re-soldering new tracks (there are two inside the pot) but I think that it is better to buy a new one.
Hope this helps and well done with the site.