Ford Focus Forum, Ford Focus ST Forum, Ford Focus RS Forum - View Single Post - Rough Idle only when the A/C is on
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Old 11-24-2012, 11:47 PM   #15
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Join Date: Mar 2012
Fan#: 96610
Location: Fort Worth, TX
What I Drive: 00 wagon, 02 sedan both zetec atx

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A lot of it is fan coming on while a/c is on. That fan really jerks idle down when motor is older. May be one reason why OEM fan is engineered to come on at a later temperature than many think normal. At one time before I put in diagnostic LEDs to show when low and high fan and a/c clutch itself came on, I thought that low fan was not coming on properly. I installed a standalone adjustable fan control set to come on at 210 and back off at 190. That thing switched fan on so much during the summer it became very bothersome at traffic lights, the engine always seemed to be shuddering from the fan kick-in. I installed the LEDs and defeated the add-on control and went back to OEM fan on temp of 230 degrees, the problem quickly became much less noticeable since fan was coming on far fewer times.
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