Morning All

Looking for opinions/advice

My Mk7 Fiesta 1.4 TDCi Titanium (60 plate) is about to turn 7 years old, and will be going in for it's annual service and MOT next week. The car is just shy of 72k miles, and, in general, is still running great (most dependable car I've ever owned!).

One thing I have noticed though over the past year is that on low throttle application at low speeds (say 4th gear, 30mph when going down a slight slope where minimal throttle is required), the car can be a bit lumpy (unsmooth - like a judder feeling). If I sit with the car in neutral, and rev the engine, it revs sweetly - no issue. If I apply just a tiny bit of throttle however - say the first 5mm travel on the accelerator pedal to bring the revs above idle to about 1000 - 1200rpm - the revs will jump about erratically. Apply a little bit more throttle, just beyond the initial bite, and it's back to being smooth.

Is this likely to be my accelerator pedal itself that is getting worn at the initial biting point, or could it be something else?

Best regards

Stuart

Might just need the injectors to be cleaned out a bit - when did you change the fuel filter etc?

might be dodgy throttle pedal.  throttle pedal is electric.  a voltage goes into it and a different (lower) voltage goes out according to the throttle position. if the internals of the throttle pedal (where the wiring leads to) do not work smoothly then the voltage going out of the pedal to the ECU (the computer that controls the engine) does not rise smoothly.  I am not saying it is that but it can't be ruled out from what you describe.  I would imagine there is a way to test it with an ohmeter to see if resistance changes smoothly but I could not advise you which wires.

1 hour ago, m1tch said:

Might just need the injectors to be cleaned out a bit - when did you change the fuel filter etc?

Hi m1tch. I have been toying with taking the car for a Terraclean after its service. The engine however is otherwise quite responsive which is why I don't think it's the injectors (I know the injectors can be an issue on this engine, but I haven't suffered any of the other various 'symptoms' that people often quote). Fuel filter was done last year - I usually go over the top and have it replaced every 2nd year year rather than every 3rd.

47 minutes ago, isetta said:

might be dodgy throttle pedal.  throttle pedal is electric.  a voltage goes into it and a different (lower) voltage goes out according to the throttle position. if the internals of the throttle pedal (where the wiring leads to) do not work smoothly then the voltage going out of the pedal to the ECU (the computer that controls the engine) does not rise smoothly.  I am not saying it is that but it can't be ruled out from what you describe.  I would imagine there is a way to test it with an ohmeter to see if resistance changes smoothly but I could not advise you which wires.

That as my thinking - basically the accelerator pedal is just a potentiometer, and perhaps the top end of it is either worn or dirty or something. 

The garage I'm taking it to for it's service next week is a Bosch approved service centre. They claim they can do a diagnostic to check this out, but I admit I'm very skeptical that this will find anything.

most of my work on cars was many years ago (20 plus years) so I have never examined one of these wired throttle pedals. They must be very easy to remove - a couple of bolts and one wiring plug perhaps? once out, can it be easily opened up?  perhaps there are three or four philips screws to access the internals which I am guessing has a coil with a contact that slides up and down the coil as the pedal moves. You might find it is dirty / worn/ dry and needs a smear of vaseline on it (like I did with scalextric throttles as a child). I am guessing a bit.

been trying google to find about dismantling throttle pedals. not a lot on there - perhaps they never go wrong or perhaps they are sealed (glued together) and can't be opened up without breaking. I cam across a galaxy pedal which someone unscrewed to get apart and it showed contacts sliding along carbon tracks (not metal coil) so perhaps none have a scalextric type metal coil - too old technology perhaps.  I would NOT suggest vaseline on the carbon tracks. 

http://www.forum.fordmpv.com/smf2/ford-galaxy-reference-library/galaxy-accelerator-pedal-removal-and-cleaning-(vcds-fault-code-00777-18047)/#sthash.QfuGfJ7z.dpbs