davermz450

Hey yall Im getting desperate. 2008 F150 4.6 w/ 127K. When ever I turn the AC on it causing the truck to throw an P0300. Ive done all the starting points to deal with a misfire, COP, plugs, cleaned MAF, blah blah blah. Everyone keeps telling to do that same stuff over and over but this whole winter it never missed but now its getting warm and the 0300 is back. I am so lost!

Dave

RLXXI

Need to check and see if it's on the latest calibration level. Unfortunately the only way to do that is take it to a dealer or someone with IDS.
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davermz450

Called ford again today to ask about the calibration and a master tech said that he has had a couple of trucks come through with the same symptoms and he said a diode on the PCM is probably smoked. Do you think a new PCM would fix it?

RLXXI

Anything's possible with electronics. If I had your truck in my stall I'd do a calibration update check first.
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fang2015

We had a similar problem with our 2007 F-150 - 5.4 engine. Ran OK until the AC turned on and then idled rough. Our independent shop worked at it and eventually gave a tentative diagnosis of the MAF sensor. Went ahead with the replacement (not a cheap sensor) and it ran some better but still not right. Mechanics said it could take a while for it to smooth out. And it did. Running well again.

Don't want to suggest throwing expensive parts at a problem, but that is our history of a similar issue.

ReaperHWK

If that's the case for the OP instead of replacing the MAF just get some MAF cleaner and clean it up, could be dirty.