SoonerFX4

I have an 04 FX4 w/ a 5.4 and 125K miles. A couple of days ago while driving it began to idle very rough and felt like it was going to stall. As a pulled into the driveway the check engine light was flickering. I hooked up my reader and got P0303 (#3 Cylinder Misfire) and P0316 (Misfire detected in first 100 revs). I changed the #3 coil and the injector and it still was rough but the codes and light are gone. Changed the fuel filter and no change. I took off the throttle body and cleaned it. It helped a little but it still has a very rough idle and is slow to accelerate (once it gets going it seems to be ok, but sounds like it is going to die when I stop). I also had the plugs changed 3 months ago. I noticed when I took the TB off that the flapper was not sitting flush (should it?) there is a small gap and does anyone else have any ideas on what I might be able to do before throwing a new TB on it? I also vacuum checked it and it seems ok on vacuum (no leaks). Thanks for the help!

Additional Info: Let the truck run for about 5 minutes and I hear hissing coming from the EVAP canister on the firewall. The sound changes as I move the canister around. Is this normal or could this be a cause for my problem?

allinon72

Any vacuum leak will cause misfires. I'm not sure about the EVAP area but you should not be getting any vacuum leakage anywhere.

brad.fx4

maybe try disconnecting the battery for about 10 minutes. then let the computer "relearn" its idle. there are step by step instructions in the back of your manual. its worth a shot, its free after all. In my personal expierience, i had this same problem you are talking about minues the misfires. It turned about to be clogged catalytic converters. i hope your fix is cheaper.

As for yout throttle body, its normal for the gap, and for the flap no to be totally flat. If im not mistaken it sits that way on idle, letting air through.

SoonerFX4

Thanks Brad I hadn't thought about that yet with all the parts I changed. I'll give it a try and post the result. Thanks again.

SoonerFX4

Ok, so I disconnected the negative terminal and waited the ten minutes. When I fired it back up it sat at about 1200 RPM. I gave it some gas and it dropped down to about 750 RPM (normal for my truck), but it was still rough idling. Gave it some gas and it shuddered up to 2500 RPM and then it went smooth. On the plus side when I let off the gas the truck did not sputter and try to die. It returned to 750 RPM and began to rough idle again. Not sure where to go from here. I hate driving it with it not running right for the fear of causing more damage. I am considering changing the throttle position sensor before I go after the whole throttle body. Any additional advice or guidance is well appleciated. Thanks.

lariatboy

You mentioned plugs were changed recently. I would urge you to pull them out and check for fouling, then retorque them to proper spec. I've seen way to many guys roll in with similar problems and it was just a loose plug that was obviously throwing the compression of enough for a rough idle, but not enough for a code to be thrown. Your canister purge valve should not be active under normal conditions either. They do wear out, and are not that expensive either.

brad.fx4

check what lariatboy says, if that fails...seafoam it? Its all i can think of :S

Especial86

iTrader: (1)

Sure starting like a Vaccum leak to me too..

Disposablehero

FYI...There is a proper procedure to help your truck relearn its idle. Please see https://www.f150forum.com/f72/batter...rocess-133736/. You can also find it in your manual as well.

Best of luck.

kanga2311

You are you having some odd issues. It make take a little while to diagnose your problem. First I would check all the spark plugs for fouling(change to motorcraft if your not already using them) and make sure you use di-electric grease on the COP boots. You should also check the FPDM( it's above the spare tire) for excessive corrosion or holes. And I would agree that you should run seafoam through the intake(warm the engine, find the vacuum line from the brake booster, put the line in 1/2 to full can of seafoam, let it pull in the seafoam, shut off the engine immediately, wait 15 minutes, make sure you put the vacuum line back on, then start it and drive it like you stole it. You should see a lot of white smoke, that's the carbon burning). I do the seafoam with all my vehicles now. They all run smoother afterwards.