Just bought my 91 f250 460 e4od. Got it for $500 from a girl on craigslist. Truck was her dads, he passed 2 yrs ago and she just wanted it gone, and needed rent money. She was asking almost a grand, and I asked her whats her bottom dollar, she said, $500, just take it, it needs soooo much work.
So I took it.it jas 220k miles on it. The body and interior are relatively clean, and only minor rust. Its Ford YY colonial white. Anyways, to the point. Ive read the Dtc codes and going by those ive changed the IAC, TPS, and o2 sensor.
I also replaced the fuel pressure regulator and have 33psi idle, 43 vacuum unplugged. Ive done many hours of work so far cleaning, replacing, adjusting, oiling, and so on. Ive got it to a point where it idles almost decent, and runs VERY strong. Shifts fine, no slipping thus far. Set timing by disconnecting spout, and set it at aprox 11deg. Btdc. So down to the question. It still has a slight miss at idle and throught the rpm range, but runs great otherwise, no more bad dtc codes after my hard work. The prior owner suggested that I clean the rear tank before filling it, as she could never afford to fill it. I sniffed the gas filler tube and it reeked of varnished, bad , bad gasoline. I mean BAD.
Just got done removing the rear tank, rear pump ruined, rear tank ruined, rusted and leaking through. Tommorow I will get a new tank and pump. Could this nasty rear tank have been causing my crappy idle? Even thouh I never selected the rear tank? Could it bleed through with bad gas? If so, it may run fine after installing all new stuff.
Thanks

 

I don't think so you would have noticed fuel transferring, try clearing the computer. it may still be applying corrections for the old items that you had replaced. Disconnect the battery ground for 5 min...run some injector cleaner...vacuum, PVC, air cleaner etc all is good?