2003 Fiesta 1.4 Zetec idle problem.

Hello all. I have an old Fiesta which, for some reason, I've got attached to. It has always served me well, but it now has a problem which is causing much embarrassment It runs fine when warming up (still in open loop, I guess), but when the idle has settled down from its initial 1200 RPM, it tends to go very low, about 500 RPM, and will often stall, which results in a lack of power steering (hence the embarrassment). My first inclination was to check the PCV valve and hose - the hose is fine, but I assumed the PCV valve was faulty since I could blow through it both ways. I replaced the valve, but a new one does the same, so it wasn't that. My guess is that it is not even a valve, since it is called an 'oil separator'. I cleaned the throttle body, and tried to test the throttle position sensor, but I guess this is a hall-effect device, since I could not get any sensible variable resistance measurements such as I might expect from a potentiometer. I guess it might be a vacuum leak from elsewhere, but this thing has a TMAP sensor (which I have cleaned), which I'd assume would take care of that. There are no codes stored. Does anyone have any suggestions of what I ought to look at? I have Forscan and a recommended connector, but I'm not sure which traces are going to be the most use. My front O2 sensor fluctuates around 0.45V as expected, and the rear one is mostly steady at 0.9V, with the occasional drop. STFT is up and down around 0. MAP is 120 KPa with the engine not running, and shows what I guess is an expected vacuum range when driving. All this seems normal, so what ought I to be measuring when I come to a stop, and the idle starts to hunt?

The 2003 Ford Fiesta is an OBD-II vehicle with a Data Link Connector (some call it a Diagnostic Link Connector) which allows communication with the PCM. The systems problem you are describing is best diagnosed using real-time PCM data. What we are looking for is when a commanded value is not achieved, like idle speed. Also, if we look at the fuel trims and HEGO signals we can tell if the fuel delivery system is operating properly.

The diagnostic process goes something like this; if fuel injection delivery and magnitude are correct and there are no misfires detected, then there is a systems feedback problem. Meaning either a sensor or an actuator is not working properly, and because no DTCs are present the failure is within normal operating range but skewed by some offset.

Hello Mark, and thanks for your reply. Unfortunately, the car has suddenly (not gradually) become a crank-no-start. I am not going to assume that this new problem is connected to the old one, since the change was so drastic. And I still have no codes to help me. I have started a new thread, since I don't want to present you with a new problem you weren't expecting when you offered your helpful reply

If you disconnect your battery, put the car in neutral on level ground with wheel chocks, and see if there is a way to inspect the CAM rotation when you bar over the crank manually with a wrench in the proper engine rotation. All you need is a way to see the CAM when you move (bar over) the engine CRANK, either through an inspection or adjustment plug or maybe by removing the CAM sensor. To me the sequence of events for a bad cogged timing belt was it first skipped a cog (tooth), engines timing is now off car loss of power, then it broke completely, engine cranks but will not start.

Thanks again for a reply. I believe the cam timing is okay. I have been going through FASTEC, and reached cam timing after everything else. I have the Ford timing tool, with the peg that goes in the back of the crankcase, and a flat plate that engages with slots at the end of the camshaft. When I first put the peg in, the slots were too low (although they were 180deg out), so I could tell the crank needed to go another turn. When I'd done that, the slots lined up perfectly. So, I'm sure that the cam timing is okay. Going through FASTEC, I haven't been sure how to check Air and Exhaust, although I reckon the Exhaust would have to be really bad for it not to even attempt to start. I have the air filter off, so I'm sure it's getting air, although the throttle plate only opens a small amount. I suppose this is normal when it's cold.