2000 Peugeot 206 engine slows, then power comes in, then slows then runs normally.

Basically I have had to emergency buy a car against my better judgement the best one I could get today was a Pug 206. I've had two from new when they first came out and all three have the same problem - I hope by now someone has the answer.
In all three cars the same problem: the car starts fine then after around 10 minutes moderate driving and not always whilst accelerating, the power will drop, slowing the car significantly for a second or two, then power will come in, obviously if on a busy road one tries to counter the slow period by accelerating gently so as not to worry cars behind however when the power cones in again acceleration is overstated and obviously this can be dangerous for motorists in front! The Engine Warning light comes up orange, each time but then bizarrely goes away again.
I remember this was a particular problem for Peugeot in my new cars before and they never got to the bottom of it but surely by now someone must have an idea??? Please help! Thanks.