I had a similar problem on my '97 1.8 Mondeo. Taking the ISCV out and giving it a good clean up with carb cleaner helped for a few weeks then it started happening again. I sold the car before I replaced though.

You might want to check the plug gaps, if they are too big then it can cause the revs to drop too far when returning to idle before it picks up again. Also if it's on it's original leads chances are they are shagged by now.

HTH

Martyn