I will try to keep this short but have done alot. 98 F150 with 4.6 liter. was on 300 mile trip when first got light, code was 0171. Installed injector cleaner and dorve back home, truck ran fine. Pulled codes again when got home and had 0171, 0174, 0503. Read on here about possible causes, so pullled maf and cleaned. Reset computer and drove. Light back checked codes 0171, 0174, 0503, 1100, 1500. Pulled all air intake hoses cleaned maf again, replace fuel filter, air filter, cleaned IAC, Cleaned throttle body, cleaned air temperature sensor. After all this drove yesterday evening about 20 miles no light or code yet but now lopes at an idle like has racing cam. Sons truck he will drive today see if it throw another code. But not sure why idle is so bad now, is there a way to check operation of IAC? Also I know 0503, and 1500 are on speed sensor, haven't worried with it yet because figured would try to fix emission codes first, Could they be related?
Thanks for any help yall can shed
David

 

The IAC isn't really cleanable, except for to see if it affects the way the truck idles. If it has gotten worse, then either you have knocked some dirt loose and now it is affecting it even more, or something was damaged when you cleaned it. You should only use carb cleaner and compressed air. If it gets a little better, then replace it for a new one. Also, the MAF is REALLY sensitive. I haven't done mine yet just because I am concerned about damaging it. Check to make sure in all this work that you have done that there are no issues with any of the coil packs as well.

 

Yeah was very careful with maf, just cleaned with crc carb cleaner, elements look good, also just cleaned IAC with same, think coil packs are ok, thing runs like a champ now, no misfire of cylinders just that lope at idle, when I was a kid used to install cams to try and get this idle Guess need to break down and buy a iac just seemed weird that it really ran fine until after we cleaned it.
Thanks

 

Yea I tried to go with just a cleaned IAC, but it only lasted a couple of weeks. At least they aren't too bad. I only paid about $70 for mine.

I know what you mean about changing the cams for the lope. Back then it was cool and meant you had some hard core hampsters under the hood.

Check to make sure your vacuum lines are OK as well. A split line can also cause you idle probs.

 

Ok thanks, figured I would get a new pcv and boot on the way home today put that on too.

 

Recheck all the work you did to ensure it was all put back right. could be something you missed like the gasket for the TB got messed up or something like that. could not hurt to check. Or like BillyBob69 said maybe a vaccum line accidently disconnected or something.

Lance

 

Ok guys, just wanted to say thanks for all the help. Finally went to replace pcv valves and elbow and found vacuum line off on passenger side. Reinstalled and runs great. Boy put a couple hundred mile on it this weekend and no lights or codes, other than that speed sensor, guess we will tackle that this weekend. Anyways just wanted to come back say thanks, I have always owned diesels, have two superduties now tried to talk boy into buying one, but he wanted F150 go figure
Thanks again