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Mitsubishi Starion diagnosis & fix

At the end of last week I made a start at looking in to why the Starion engine would not idle correctly. The idle is entirely controlled by the ECU controlling a stepper motor with inputs from various sensors (engine temp, barometric pressure, throtte position, engine speed, etc.). With the engine running and idling at 1700, if pressure was applied to the throttle (enough to lift it off the throttle switch) the ISC would then have a mind of its own, reving the enigne and then slowly dropping abck to 1700. I checked all of the sensors, connectors, vacuum system and even the ISC, as they all looked ok, and the owner happened to have a spare car, I swapped the ECU and that did the trick. Mostly anyway. The engine would now idle at 1000 rpm but it had a moment on initial start and, once I'd found the diagnosis plug and fabricated a lamp to attach to it, was showing code 7, engine temperature sender. As it wasn't the sender, which was acting normally, I checked continuity between sender and ECU - there was none. I made a rather long jump wire between the 2 points and it fired up as I'd have expected and settled into a steady idle as it warmed. Now all I have to do is break into the loom in the middle, find which end the fault is at and let in a wire. Having looked at the back of the bulkhead and not been able to see where the loom exits this might not be as easy as it sounds.



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