Uh oh spagettio....
I may have been running mine on Sainsbury's Super since I had it - I am aware that it's only 97 RON but thought it was basically BP super.
Yikes!!!
Oh, and BP havn't supplied Sainsburys for around 6ish years now - they just fill their fourcourts with any 'unbranded' and additive-free crap. So whilst their Super may be 97RON - it has bugger all additives to keep your fuel system and engine clean.
I can't comment what the last owner has run the car on but she was an 'older' lady shall we say and I can't see her as having been filling up with super unleaded to be honest.
OK, now some 'truths' about fuel useage are emerging - get yourself two tins of VWs latest petrol fuel additive - G 001 770 A2 - bung one whole 90ml can in a fresh tankful. Maybe best to do this after the new fuel filter.
I can get Shell V-Power or Tesco Super where I live - I'm guess Tesco ain't much cop either as it's supermarket fuel so I'll start filling up with V-Power from now on.
Tesco Momentum 99 is just as good as Shell V-Power. It has been proven in independent tests to be slightly better than V-Power, and spanks BP Ultimate. Tescos Super Unleaded isn't like other supermarket fuels - it is made by
www.GreenErgy.co.uk - the UKs fourth largest road fuels company, and the pioneer of B2.5 and B5 bio fuels.
And it is the official fuel of the British Rally Championship.
Could that point to my problem then - and will the damage be lasting?
I'd strongly point to cr@p fuel being a major contributory factor with your issues.
And lasting damage? Its hard to say. Probably more damage was caused by the old dear who owned it before. If she was on LongLife servicing, did lots of short journeys (cold starts, overfueling, oil dilution, etc), never spanked it to burn off contaminents in the engine oil - then that is likely to be more damaging. Do you have the service book? Was it on LongLife servicing? How old is the car and how many miles has it done?
I ran the car when I had it back from the garage on V-Power with Forte in it and the cold start never changed from what it is now, not has it changed since I've put a few tanks of Sainsbury's super in it.
To be honest, your engine will need three or four starts from cold to allow the ECU to re-adjust to the higher octane fuel - and I doubt you'd fully run your tank dry - so the V-Power is still gonna be diluted with the crap fuel left in the tank.
And what specifically was the Forte you used? Got a linky? Based on the cars' history, I doubt one tin of fuel treatment will have any chance of majorly cleaning your fuel system.
Just like it probably got 'progressively crap running', it will probably take maybe four full tanks of decent juice, and a couple of cans of fuel cleaner additive to get it back to normal.
HTH