9

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?

|improve this question
  • 1
    it's based purely on engine RPM and ECT. does the car misfire? do you have access to a scantool to check fuel trims? Id suspect a vacuum leak or misfire. – Ben Apr 13 '16 at 21:01
  • 2
    @Ben - Didn't the Freestar have the issue with the bolts holding the lower plenum onto the block wearing out and causing a vacuum leak? I don't remember if it is the Freestar or the Windstar which had this issue. There is a fix kit for it. – Pᴀᴜʟsᴛᴇʀ2♦ Apr 13 '16 at 21:21
  • 2
    @Pᴀᴜʟsᴛᴇʀ2 It was the Windstar with the 3.8 IIRC The rubber material on the bolts is what went bad. – Ben Apr 13 '16 at 21:36
  • @Ben - That sounds right. – Pᴀᴜʟsᴛᴇʀ2♦ Apr 13 '16 at 22:29
1

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.

|improve this answer
  • This "fix" seems highly vehicle-specific. Do you have the link to the page? – Zaid Apr 28 '16 at 6:08
  • Zaid-I read it tonight and can't seem to find it -sorry – Old_Fossil Apr 28 '16 at 6:26
  • This is a common fault, and yes, a TPS is exactly that: a variable resistor. The centre rotating part can become floppy, and/or contaminated. – Bevan Jun 14 '16 at 20:10

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.