I had this exact problem last year but it was also causing it to stall, and being an automatic was giving some right hassle. Anyway the problem is caused by dirt in and around the air intake on the top of the engine. I took mine into the dealer and paid £70 to get it sorted, but also watched the gut doing the job in case it happened again. All he did was remove all the air intake pipes and remove the top housing (not quite sure what you call it but it's the thing that has the butterfly valve in!!), then cleaned it all out with some carb cleaning fluid, he paid special attention to the little holes in and around the side of it making sure they were all clean. Anyway he put it all back together and it's been perfect since. I can try to explain further with the help of digital photos if you send a mail to steveatpilley@yahoo.co.uk. Hope this helps.
P.S. I got told it was EGR valve at first which cost me £60 and this made no difference, so be cautious.
steveatpilley@yahoo.co.uk, October 2005
