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I have a 2004 Freestar with 240000 kilometers on it. I have had problem with the engine surging at about 1100 rpm or high idle. No check engine code is logged, I put it on a Ford computer and there were no results. After I cleaned the MAFS and IAC valve the vehicle ran good for a week or two. I found a loose wire on the IAC valve and fixed that, the engine ran well again for a while but then the IAC Valve would start cycling when the engine was hot. I thought I had it so I changed the IAC valve. Started the car, idles perfectly and revs up but as soon as I put it in gear the IAC valve starts to cycle much worse than the old one so the valve itself is working fine and I don't think that is the problem.

Does anyone know which sensors are feeding the computer so that it is sending a message to the IAC to make it cycle like that?

Bevan
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Dave Hodgson
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From my research on surging idle..A possible solution-TPS(Throttle Position Sensor) connector. I read on a diagnostic webpage that this guy disconnected and then reconnected it and the problem was solved for 3 weeks. In theory it makes sense when the ECM loses the input from the TPS sensor it falls back on a default setting until the TPS is reacquired. Maybe the ECM takes data from other sensors. If I were to speculate that the throttle position sensor is a variable resistor with a speck of dirt on the resistive element that would cause a lack of signal intermittently.

Old_Fossil
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