Car wont exceed 4000 rpm

Numerous possible causes , i.e could be fuel filter needing changed .

more likely to be in limp mode. have it plugged in and diagnosed. could just be a simple sensor fault. hope this helps!!!

Another suggestion, could also be partially choked cat / exhaust .

hi there i sorted my friends fiesta out yeterday he had the same problem we narrowed it down by swopping sensors from both of our cars untill we found it.we ran a fault finder on the car each time it came up with fault (p10171 lean at bank 1) after deleting fault and taking the car out for a run after it was idleing for 10 mins it sorted the problem out after we replaced the air flow meter before the air filter you have 2 tiny resistor sensors in the flow sensor 1 is lean and the other is rich if one of these are damaged or not working when you go to drive the car over 4000 rpm it will drop back and the ecu will compute there is a problem and cause the shutdown to prevent damage to the engine once you replace it with a new unit around £45.00 i wouldnt advise a s/c hand one unless your short on cash it maybe broke. if you disconnect battery neg for around 2hrs it will erase code out of ecu then connect back when the sensor is replaced and run it for 10 mins on idle so ecu can adjust settings then take it out and it will be cured if it isnt check wire harness in engine bay clean all connetions on the harness i hope this helps we spent 3 days sorting this problem out and and sorted it