I recently bought a ford mondeo zetec reg 03 1999cc and now have problems which garage cant resolve. after a while on motorway car decelerates and cant get above 30. But when garage has a look they cant replicate the fault after its been sat overnight. I have been towed back by breakdown company who said the diagnostics said its was something to do with a fuel sensor. Garage cant find that to be the fault.
Can anyone give me some idea what should be looked at. Please

 

The problem you have is simple but its in your tank so no one will find it!!
There is a little mesh filter on the fuel pump.This gets blocked with tank grime but usually clears itself when the petrol its sat in washes around it causing an intermittant problem.
What happens is when its blocked or very grimey it causes a drop in fuel rate to the pressure reg-the chrome ufo thingy near the lh side of the cam cover-(focus). This in turn causes a loss of pressure at the fuel rail and spluttering under load/bad idle.
Only cure it seems is to take it out and clean-redex awesome for fuel line etc but wont clean this mesh-ive tried!! Best of luck,
DUDOCO.
P.s. you may have no fault codes showing.Its an arse of a job but itl save you a fortune at the garage! Trouble is if they dont see a code they dont see a fault at times ECUs!!!!.