I have a 2004 Ford Fiesta 1.4 petrol which has developed an annoying problem. While driving, it has an intermitting problem of pulling back as if it was running short of petrol, then it will suddenly shoot forwards. Sometimes it gets so slow that I have had to pull over, wait for a while and restart. I have had it to the garage several times with no joy. So far it has been on the diagnostics (no fault found), fuel cleaned out and new fuel filter, renewed core plugs, checked for water leaking onto electrics, new HT leads, new air filter, oil and filter. I also tried leaving the fuel filler cap slack in case there is a vacuum build up.

It doesn't matter whether it is dry or wet, and it seems to happen when the fuel is low. I'm starting to wonder if it could be a faulty fuel pump? But I have spent so much now I just want it fixed. Can anyone help?