C3 Picasso, petrol semi-auto box, low annual mileage, very poor cold starting

[Mish]

I have read threads on this topic but not sure if my problem is the same!

Filled with fuel from normal forecourt, next morning when cold it almost refused to start. Several turns of they key worked but when going it was lumpy, surging and ‘hunting’ as we used to say in the 60s/70s. Odd puffs of black smoke too – over-fuelling?

Put my little OBD reader on it and showed no faults.
Fitted new set of Bosch Iridium plugs.
No improvement.
Regular service agent found no fault on his more sophisticated OBD reader after having car overnight for a cold start early morning. So thought it is fuel pump but tank needs removal to replace it – but the fuel pumps OK when driving the rest of the day!
Went for full diagnostics at PSA distributor with a workshop full of new toys.
They had the car for SIX days on diagnosis. Said there is no fault showing so think it is water in the fuel. £600 total for diagnostic and tank removal/emptying is too much for this pensioner.
Back at regular service agent they said they regularly drain water from tanks in-situ by pumping out and checking all removed using fibre optic scope.
When finished they said the fuel removed had a weak smell of petrol and not as strong as petrol is usually. This may be due to my use of Wynn’s ‘Dry Fuel’ to absorb water, which I have used successfully before on diesel boat engines. (This might confirm that there was some water in the petrol). They say there is no filter on this engine, so could not make a replacement for peace of mind – really!?

Still no improvement: starts badly, revs surge when cold, odd puffs of black smoke. I have put in half a tank of fuel from a different forecourt. Interestingly the source of the fill-up prior to the trouble, when approached, told me that they have sophisticated water monitoring sensors on their storage system and would not entertain that there is any chance of storage condensation. Therefore I should complain to trading standards people if I think they sell contaminated fuel. Confirmation of other complaints to trading standards would cause them to have second thoughts. This fuel by the way comes very fresh from the refinery 12 miles away!

So if there is no sensor showing a fault, would it still be the fuel/coolant/air temperature sensors or idle valve still giving the trouble as suggested in other threads? Your collective opinions would be valued, thanks.
m

[Mish]

So 20 views in 5 days but no suggestions. So i take it that I should take the temperature sensor and idler valve route then? Thanks to all who have helpfully viewed my problem. I will report back when I have an outcome.
m

[Hell Razor5543]

Sorry I have not been able to offer any advice, but I have no C3 knowledge. You might want to allow for the fact it is Easter, and some of the more knowledgeable members may be away on holiday.