Hey guys, so long time lurker on here and that has usually fixed my issues. However, this time can't find an issue same as mine.
I have a 2001 5.4 f250 truck runs great aside from I've had to change the iac valve last 3 years for some reason.
current issue is it feels like it's misfiring in a few situations. It shakes truck at idle, and while on throttle if between 1 and 2k rpm but not while coasting.
So background on the issue, I was driving on hwy one night during blizzard while I already shouldn't have been on the road, put truck in ditch. Was able to finally get back on highway but may have high centered. Parked for 2 days after I got where I was going. During those 2 days it also went from +10C to -30C so not sure if that caused issue with a gasket or not. I haven't been brave enough to physically look under truck but I don't think that would matter because if I high centered and broke something it wouldn't be only an issue between 1 and 2k rpm and only while pressing gas pedal.
no codes and nothing looks out of ordinary in live data. At least to me, not having a ton of experience with live data.
any place you guys would start would be helpful.
Edit* fuel mileage had gone also gone from 500 to 550km per tank to max 400km. Plugs and coils were all changed last year. Last month had to helicoil 1 plug that blew out on highway so 1 plug and coil is different brand than rest if that would make a difference

 

I'm lost with your description and the events as you lay out. Have you replaced the IAC 3 times or just one in the past three years?

This sounds like nothing more than a cylinder misfire and if that's the case a DTC should have been triggered. The low temperatures you experienced would not have an effect on the engine operation. If the plugs were specified for your year and engine that shouldn't cause significant MPG changes---have you checked the long term and short term fuel trims?

 

You should be able to see misfires in the live data which will tell you if you have one cylinder misfiring or general misfiring.
It takes a lot of misfires to set a code for even one cylinder and you may never get a code if the misfiring is all of them.
Either way find it soon before the raw fuel going thru the cats ruins one.
Also, when it's convenient you should consider replacing the helicoil repair with a Timsert or comparable insert.
Timesert has a special insert for repairing heads with helicoils, check out their website.
Also, find another Motorcraft SP479 plug to replace the different brand one.