307 1.4 loss of power

[treeman]

2003 Estate, 68,000mls I've got a problem with power loss on any sort of incline. Foot can be flat on the floor and acceleration just gradually drops off. There are no warning lights whatsoever. Main Peugeot dealer seems stumped and reluctant to investigate in the absence of any diagnostics showing, despite having experienced the problem for themselves. They did change a wire that leads to the Air Mass Filter? which made it ok for a day then it lost pawer again, took it back and they re did the wire and was ok for two days!
Having googled that it may be the particulates filter, I tried thrashing it in fourth gear for ages , made no difference just ended up pulling into service station with spoke coming from the bonnet.

Any thoughts welcome please, other than driving it off a cliff, though it would probably never make it up the hill