I'm having the same problem with my 306.
A couple of months ago, it began smelling very strongly of petrol, soon after, it started to bunny hop, stall (unusual since it's an auto!) making popping sounds, almost like backfiring, doesn't respond when I put my foot on the accelerator, (this doesn't always happen, but when I'm at junctions, roundabouts, going slowly basically), it's worse uphill too, revs very high, and sometimes runs away with me.
When the car gets moving, it's fine... it's more at take-off, although even when it's moving it's not 'right'.
The diagnostic light very occasionally comes on also.
I took it to the garage, and explained everything. The guy couldn't figure it out, at all. Eventually called out his mate with a diagnostics machine, who checked for errors. The computer threw up some random errors... the guy cleaned my... somethings, cam heads i think, the computer was reset, and it ran like a dream... for about... 2/3 days.. then went back to running really badly. It was then I noticed there was a small fuel leak at the rear tyre, right by where you fill the tank. It only really drips right after you pump petrol or if it's got more than a tenner in the tank... so long as it's not been parked at a severe angle.. but it's still there. I went back, told the guy that it was running crap again and pointed out the fuel leak. he didn't seem overly concerned. he took it for the afternoon... basically got the diagnostic machine out again, reset the computer, and nothing else. Car ran fine... for about... a week... then went again...
I've had the engine reset about... 4 or 5 times now... each time, it's runs fine, and it lasts in this state for varying amounts of time, but inevitably, end up running like a bag of crap.
The fuel line is STILL leaking, despite my asking him a bunch of times to fix that... and apparently now it's a common part to split and there is a big old backup of orders for it....
The latest time the computer was reset, it threw up an error with the lamba sensor... which I understand might cause the problems... so he's ordering a new part.. although this is the first time this error has been thrown up, so I'm starting to think he's grasping a little....
So, it is either
a) fuel line split
b) faulty engine management chip
c) lamba sensor
d) something completely different?
I want my car back!