UK Car Repair: Vauxhall combo van 1.7DI 04reg, vauxhall combo van, crank shaft position sensor

Question
Hi, for the past 3 weekends I have had a problem with my van, I drive off in it and after 2/3 minutes the engine goes into 'go slow mode' and the exhaust emission light/engine management light comes on.The first time i paid to have a diagnostic check done, which cleared the problem (apparently) but gave 3 codes.  The mechanic recommended that if the problem reoccurred then first job was to change the ckp (crank shaft position)sensor.  After spending a further £130 this fixed the problem.....so I thought.He advised that if the problem still came back it would necessitate a new egr (exhaust gas recirculation)valve.  I have noticed that this only happens at weekends (when the van has been unused for a day or two).  It also happens to be after I fill up with diesel on a Friday, after running very low in the week, and also at the weekend the van is parked on a slight downhill incline.  It sounds daft but i am certain it has something to do with the problem, or at least an aspect of fuel level/pump/filter has something to do with it.  I cannot afford to keep paying the mechanics to 'experiment' with my van as I am loosing money by not being able to use it.  I would really appreciate any help, advise or information anyone can give.  Thanks. enquiries@fmelectrics.co.uk

Answer
These are complicated problems to deal with. The fact that it is going into "go slow mode" means it it sensing a more serious problem than a Crank sensor or EGR valve.  The problem may be in the ABS or traction control systems.  A faulty ABS sensor often causes this reaction. As for the "weekend conditions" you describe, change them, fill up sooner, start it on the weekend,  park it in the opposite direction etc.