Hi,

I wonder if anyone can help. My 2006 fiesta Zetec S has recently been having issues starting which seem to be getting worse. The car starts for a few seconds and then stalls. It does this on 4 out of 5 attempts to start. Once it's running it seems to be fine, however what started out as once in a while now seems to be consitent every time I start. I had someone come and have look who  plugged a computer in and no errors were reported. They suggested that it is most likely the immobiliser getting out of sync and suggested trying the spare key.  However the fault happens with the key also. I have noticed that the remote central locking has recently been a bit sluggish I.e sometimes takes a few presses on the fob before the car locks so the imobiliser theory did seem to check out, however given I've tried the key without a fob this doesn't seem to be the case. Another theory was the MAF sensor but I assume given no errors were reported that this is also unlikely so I'm a bit stuck now as to what might be the issue. I obviously could take it into a garage but would rather go in with some idea of what the problem is before hand if possible so any suggestions would be much appreciated. 

5 hours ago, Bilbowski said:

They suggested that it is most likely the immobiliser getting out of sync and suggested trying the spare key.  However the fault happens with the key also. I have noticed that the remote central locking has recently been a bit sluggish I.e sometimes takes a few presses on the fob before the car locks so the imobiliser theory did seem to check out, however given I've tried the key without a fob this doesn't seem to be the case. Another theory was the MAF sensor

Hmm, a bit woolly there!

The immobiliser will stop the car from starting at all, if it is out of order. Once started & running, the immobiliser will not stop the car, for safety reasons. The central locking (remote control) is not really linked either to the immobiliser, or to any engine functions.

If the car is the 1.6 Petrol version, it does not seem to have a MAF, it has a MAP (pressure sensor) instead. Non-Turbo engines only need one or the other. (If it is diesel, then most of the following will be wrong!)

However, calibration of the MAP could be a cause. A moderate calibration shift would not cause DTCs (error codes), but could cause problems at start up. To start the car, either default values or the MAP will be used to control the injectors. Then once running, the O2 sensor(s) will take over, and fine tune the air/fuel mixture for optimum operation. During this take over, if something is wrong, the mix could go too far rich or lean, and stall the engine.

But other possible causes are fuel pump pressure regulation, fuel filter, injector performance, O2 sensors, exhaust system leaks, or air leaks into the inlet manifold. All of these are involved in fine tuning the mixture. Observing the fuel trim values via the diagnostic connector might show whether the fuel trims are out of normal, and which way.

Ignition seems less likely here, if the car starts initially, and if runs smoothly through the full range from idle to full power once running.

Unless you are keen on diagnosing fuel & mixture problems, it is a garage job. Explain the symptoms carefully, and maybe suggest you think it is a fuel mixture related problem.