I have a F-150 '98, 4.2L V6. I'm having these problems after warm up:
-When the engine is started it runs fine for a few minutes.
-After it warms up, it starts to idle rough and then it seems that it wants to stall. This is with the truck parked.
-When I try to drive it, it wants to bog down at certain times making it nearly undriveable. If I drive it right after I start it is drives fine only before warming.

I noticed the first weird sign when the fuel was very low and it started to idel rough. I refueled and it went away. A couple of days after that I left my lights on and the battery went dead (old battery) and I replaced it. Now the problem started. I know the system had resetted because it the loss of power. It drives so bad that I don't want to drive it till the system adjusts itself. I had never had such a bad idle after the power was taken off.

I had them checked for codes but none came up. The said maybe the oxygen sensors might be faulty. I had changed the both front sensors a year ago for another reason. What do you think?

I appreciate any help you can offer me.
Thanks, Tpietersz

 

Try cleaning or replacing your Idle air control vavle (IAC valve).

 

Thanks Yankee7985, I'll try it out and see what it does.

 

Just a thought, make sure the MAF (Massive Air Flow sensor) connection is tight. And also, if you oil your air filter. The MAF could be contaminated but I believe yank is right