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Hi guys, I have a 2002 F115 aet with 486 hrs & it will not idle properly, it is idling anywhere between 950-1200 rpm, I am unable to slow it down unless I regulate the air flow into the ISC control valve body assy using my finger to restrict the air flow in, I have fitted a known good ISC valve from another known good running engine & still same result & also I have fitted my ISC into that other engine & it ran perfectly. I am unable to dtect any air lewak anywhere. I connected my diagnostic software & the ISC monitoring is showing 65deg before starting & then 30deg whilst idling above 900 rpm, when I slow the engine by regulating the airflow in using my finger, that ISC value increases as the engine RPM reduces, when I control the engine idle speed @ 750 RPM, the ISC value is around 55-60 deg which I believe is about correct, as this is approx the value of ISC opening when running this other engine & watching that ISC open value @ 750 RPM. I have reset throttle body sync as per Yamaha service manual & have set the TPS @ .73v, I have fitted my Vacuumate digital vacuum gauges & all manifold vacuum readings are equal. I am now thinking maybe the ECM has a failure internal on the earth side of ISC operation as I have seen other threads with ECM failures due to overheating from faulty ISC valves. I have removed/cleaned/refitted earth wires on engine wiring harness & no improvement. I am running out of ideas, what do you guys think.
Cheers Tony
Cheers Tony