Bit of a stab in the dark but if you use Torque Lite with your OBD reader you can see the throttle position as a percentage while you press the throttle pedal. It can be done without the engine running. If there's anything obviously amiss with it it might show up, kind of a long shot though
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2005 Fiesta ST - wrote off
Newman fast road cams, Fusion Fabrications custom inlet manifold, custom exhaust