Citroen Xsara Picasso after filling up at garage engine lost power

Coil packs breaking down are a common fault but usually only affect one cyl at a time .Could check air filter but may be EGR but usually tiggers engine fault light .

I have tried two coil packs to no avail engine management light is on had it checked at garage fault came up as number one sensor they changed lambe r sensor and the fly wheel sensor engine still the same where do I go next they think it could be dirty petrol any other ideas!