Hi Richard
I don't know whether what follows will be of any help.

A while ago I had a 2004 Ford fusion which was fitted with a Duratec engine. On very rare occasions the odometer or clock display, I can't remember which, showed a scrolling message saying “Throttle sensor error” and the car would drop into limp mode. So limp the bloody thing would not climb the hill where we live. Like you the fix was to cycle the ignition off and back on again and all was well for another year or so. I decided to look into the problem and perhaps clean the pot tracks. The sensors at the throttle body looked to be sealed so I left that alone. I removed the throttle pedal but that was sealed also.

While the pedal was out I made some ohm measurements between the six terminals and recorded the results for future reference. The sketch diagram shows what I found. Bare in mind the parallel resistors shown across the pot networks were calculated from the resistance measurements and might be all wrong. I could only prove that, by opening the enclosure, but did not want to destroy the pedal. The pedal was refitted but the fault re-occurred in the fullness of time but still very rare so I decided to live with it.

Some time later completely separate and unrelated to the above the MIL light came on with fault code P0301 cylinder 1 misfire. This would occur once or twice in about 50 miles and was a single blip as if the misfire was only a one off and not continuous.. The only thing that was consistent was it would occur when the engine was under load either accelerating or attempting to maintain a constant speed up hill.

I changed the plugs and plug leads but still had the fault I thought it might be fuel so I removed the injectors, built a rig so that I could fill a chamber connected to the injector with carb cleaner, pressurised with an air line to about 50psi. I then pulsed the injector repeatedly with a circuit I built to look at the spray pattern. Cylinder 1 injector performed exactly as the others and they all looked good. So like you I removed the throttle body and cleaned it thoroughly. All to no avail.

I finally found the fault was, a difficult to see hair line crack in the coil pack near cylinder 1 HT o/p terminal. I replaced the coil pack and that fixed the misfire problem.

The point of all of this is that after doing all the above trying to trace the misfire problem, coincidently the throttle sensor fault never came back for the eight years I owned the car thereafter. So you may be onto a good thing.


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Regards Tony
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