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SWMBO has just got home and has been stuck in a jam for 45 minutes. No change in engine temp but three times the engine moved up to 3000 rpm of its' own accord. Any ideas?
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Can't say for sure without knowing which engine you have (engine code on chassis plate), but if it is the ordinary single-point injector Bosch system, the most common cause (but NOT the only one!!) for this symptom is a high / variable resistance across the "throttle-shut" micro-switch terminals inside the throttle stepper motor. You can check this with an ohm meter on the bottom two pins (of the four pins) with the harness plug disconnected from the stepper motor. Should be 0-10 ohms throttle shut, open-circuit with throttle open. Typically we see anything from 15 to 1500 ohms with throttle shut, reading varying each time it is shut. The computer is thus confused about whether it is shut or not and either fails to control revs or continually increases them.
If this is the fault, new Stepper Motor is only cure, usually about £70 + VAT from a Bosch agent, possibly more from Fiat. Fitting time 10 mins.
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Very grateful adam, thanks a lot. Have printed off your response. Today the engine behaved perfectly well. On monday when this happened the car was in a stop/start queue for over an hour. Typically of course, our local Fiat dealer closed down last month! Thanks again.
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