I recently aquired a 99 F-250 Lariat with 60,000 actual miles. The truck sat for 5 years driven once a year until the last 3 in which it never moved. It had rats and coons living in it and under the hood but the body is perfect. It sat under a shed so no sun damage. After turning the crank I knew there was hope for it so I began fixing wire after wire after wire and vacuum lines up the wazoo. Took off the gas tank and thoroughly cleaned and replaced fuel pump and filter. It tried to run but not quite so I cleaned all fuel injectors and it ran smooth as a brand. New truck. Of course drained avert thing that held oil, grease or fluid and changed. Ripped out dash and interior and cleaned for days. Now we have an almost perfect truck except for one thing ( or maybe it's 2) that I can't quite figure.
It runs really smooth until I go past a certain point on the gas pedal and it starts bogging. At first it was throwing three codes and I replaced MAF, IAT, and ECT. Now no codes. It doesn't backfire it just bogs. If the AC is on when I floor the gas the AC will switch from vents to defrost and then right back when I let off. Here is a funny thing, if I stop and kill the engine and restart it will quit doing it shortly (or at least not near as bad). I figured that eliminates exhaust back pressure. I figure the ac part is vacuum related, and I figured there is a good chance that the bogging is too. I thought maybe I crossed a line when replacing all the rats had chewed but idk. Any ideas from those symptoms?

 

I don't believe that you issues are related. The IAC and egr come to mind...they may be stuck open or closed for the engine bogging.

I also think a vacuum line may be crossed.

 

I would agree that it's probably 2 separate issues, the only thing that makes me think otherwise is that the 2 issues occur at the same time and under the same circumstances. And it's one thing I've learned in life is that coincidences usually are not coincidences. Or something like that... Lol.

 

I need to find a diagram of these vacuum lines... That would probably be helpful