From another thread where the fuel filter apparently fixed an idle issue. Probably won't help, but at this point, if I am not mistaken you have already checked: Plugs, Wires, TPS, IAC, Fuel Pressure, Fuel Injectors?, vacuum hoses, MAF. May be worth it to see if its one of these weird gremlins ( O2 sensor, fuel filter), before moving on to ECU stuff.
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I understand this is an old thread but i figured for the benefit of the next person that is searching for a solution, I'd add my insights here.
I had done a valve cover gasket job and replaced the air boot due to a tear. While I had the throttle body off I cleaned it along with IACV. I replaced the PCV as well. When I got it back together, my idle was high. It's been that way for about a year. Usually when the truck would warm up after driving it around, the idle would return to the normal range. I tried resetting the ECU multiple times. I replaced the MAF. Cleaned the MAF later. Replaced the air K&N air filter. Removed the throttle body and IAC again. Everything looked good. I checked the vacuum hoses looking for leaks. Nothing there either.
Today, i installed a new fuel filter and VOILA! No more high idle. Note I didn't even remove the battery ground to do this. I just unplugged the connection to the fuel pump, ran the fuel line dry (wouldn't start actually) and replaced the filter. Happy to report no high idle. If the problem should return, I will report back.
Hope this helps someone down the road
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