Hello to everyone and thanks for having such a forum. I look forward to gaining lots of information useful to me and will perhaps even have a chance to add something useful, too. Now to my problem.

I have a 2003 F-150 with the 4.6l V-8. It has 37,500 miles on it. Just three days ago, it began to idle very roughly and acts like it wants to die unless I feather the throttle pedal. I read two trouble codes which were P0171 and P0174. I also replaced the Throttle position sensor since I thought that might have been the culprit...apparently it wasn't but so be it. I've now ordered Auto Tap and the specialty packet for Fords that they offer. I haven't yet received it. When I do, what parameters do you suggest I check on? I am guessing that I'll have to monitor the performance of the fuel injectors and I hope the program allows me to do that. I suppose the fuel pump could also be part of this problem. I don't know if any other sensors could be involved or not and don't know how to test them if they are. You can see I have a lot to learn. I am retired now and plan to keep this truck for quite a while so I figure I need to learn as much about it, beginning now, as I can. So, fire away with any advice you think pertinent and know that I sincerely thank all who take a look at my post and especially to those who make the effort to reply. Everybody have a terrific day!

 

I had a problem like this on my 97 Expedition and I had two things that were very wrong. I had a vacume leak behind the intake where the pcv valve hose goes too and I also had a more serious problem of a leaking intake gasket where the water jacket and the intake port were really close and the gasket gave way. The leaking intake gasket made it idle rough and have that distictive miss in it. couldnt figure it out till I couldnt turn the truck over one morning. Thought it was a head gasket at that point and didnt find it till I was going to change that. Good thing I did find it when I did. The vacume leak caused the worst part of the rough idle and it was throwing those same codes. If I were you I would look for that first. I hope its not the intake gasket since the mileage but thats what mine was. Hope this helped.

 

Hey Deuce, thanks so much for the tips. I still have that problem going on and it's really annoying me. Your suggestions may well help get it resolved once and for all. If I may trouble you some more, how did you go about figuring out where the vacuum leaks were and that it was vacuum problems versus something else? I am not sure how to test for vacuum. I remember on the cars I grew up with you could pull a hose and put your finger over the opening and you'd know if it was pulling vacuum or not but I haven't a clue on these newer computer-laden sleds. Are there any tricks to finding vacuum leaks like these on or in an engine nowadays?

 

You can use propane and a piece of tubing to test for intake manifold gasket leaks. Turn on the propane to a slow flow (no more exact than that...) and probe around the intake with the engine running. The propane would be sucked into the intake, and hopefully enrichen the mixture enough to overcome the extra air causing the miss. When the idle smooths out, there's your leak.
You can do the same thing with spray carburetor cleaner, but propane is not as messy.
The 171 174 codes are telling you that the computer (ECM) has tried to compensate for the leanness, but has reached its limit on both banks.
I got that information from the "Technical Information" entry at the top of this sub-forum, and looked at the PDF file for "ODB-II Codes".
tom