For the last month my '03 F250 5.4L truck's engine hasn't seemed to be running smooth. No CEL, so I'll try to elaborate the best I can. Everything I'm going to describe has been getting worse very slowly over time.

Usually when the truck is at idle I can't even feel the engine running sitting in it. Now it feels like it has a minor skip. Almost like the engine pauses for a split second. It makes a very subtle vibration from the engine now when idling. Also when I give the truck a quick rev, as the RPMs come back down and are almost to idling the engine seems to stumbles a little. This sound like it may be a slight misfire if a slight one is possible?

Now when driving the gas pedal is not smooth like it used to be. It feels a little harder to push down and has a gritty feeling. The engine is a little sluggish too. Throttle response is worse. Also a noise like a rumble of a car with an intake on it, just a little quieter from under the hood. At a stop light the engine has a light pulsing kind of vibration.

All of the vibrations I've tried to describe are not real bad like the engine is coming out of the truck. I've had two coils go bad the day after I got the truck three months ago, and it felt like the engine was going to be ejected. I changed the fuel filter two weeks ago and the old one had brown gas coming out of it, so it definitely needed it. I ran a can of Sea Foam in the gas tank this week.

These symptoms have cleared up a few times in the last week or so. One time when it got to almost 40 degrees and yesterday week for a day after I has about 100 miles on the can of Sea Foam ( maybe a coincident because it wasn't frigid like it has been). When it felt cleared up the gas pedal was smooth, throttle response was better, idle was a lot smoother with a slight skip in it, and engine felt tight with no intake kind of rumble. Does this sound like a plug/COP or throttle body problem? Truck has 113k and I'm not sure if plugs have ever been changed. I asked about the throttle body because this weekend I noticed that the throttle body behind the butterfly has a black film, stuck my finger in there and that's what came out. The inch or so before the butterfly is all clean. I'm probably going to try to clean the throttle body out this weekend if that may make a difference. I've found a good thread on how to take it off and really clean it good. I'm hoping it's not a plug problem as I don't have the extra funds for a mechanic to do them and would have to attempt them myself and pray none break off or threads come out . How do you guys think I should go about this?

 

First, pull the throttle body and IAC and clean them both. The grittly feeling pedal sounds like a TB issue. When coil(s) fail, you should notice the problem gets much worse at higher RPMs. When my 2 went, it would run fine, then all of a sudden it would miss and only reach 3000rpm. The truck would shake violently.

If that doesn't clear it up, you should start saving up for plugs. I am pretty sure you have the 2v motor and my plug change wasn't bad. I laid out my tools and parts, and it took about 2 hours to do a very neat job, torquing each plug. If you do your own, get good plugs, dielectric grease, have a torque wrench ready. I used an internally swiveling spark plug socket that just did fit in the hole, the socket didn't have space to wiggle or break the insulator.

 

Thanks for the advice. I'm going to pull the TB and IAC this weekend and clean them up. Getting the plugs wasn't going to be a problem, the labor from a mechanic wasn't really in the budget. What was the internally swiveling socket you used? The only reason I wasn't going to do the plugs myself was because of the stories I've read of them breaking off or taking threads out. Maybe I'll give them a try. I usually put atleast plugs in every vehicle I get. I'd feel better knowing this truck has new ones in it too.

 

It was made by KD tools

 

Cool thanks, I'm going to look into them.

 

If the vehicle is stalling or misfiring under medium throttle application, there may be other problems present besides a defective IAC valve. Im not too familiar with the IAC in the SD but as far as i know they are sealed units and cleaning doesnt really solve the problem and any noticable changes (if any at all) are short lived. Some one else may be able to confirm this. When a IAC becomes defective they also don't take kindly to the cold. Try hitting the IAC with a hair dryer to warm it up and see if you problem decreases.

Don't rule out a possible vacuum leak as well as other vacuum operated systems including the PCV valve. as these can mimick some simmilar results as a bad IAC. Clean the TB as suggested as well as the PCV and Don't forget to clean the MAF sensor as well.

 

The IAC is not sealed and will get just as fouled as the throttle body. But where the TB has a butterfly and only moves against the crude at small points and less contact as the plate opens. The IAC is a piston type valve (I believe it still is), the piston moves in a sleeve to expose the plenum port. As the sleeve gets cruded up, the piston gets jambed and stuck. Most getting stuck in the idling position and not the starting.

In any case, it does need to be maintained. Not so much a defect as something you have clean so often.

 

IAC? Not all of us know what these abbrev's mean. Help us dumba***. ha ha

 

IAC = idle air controller

 

Pull all the COPs and check for water/dampness/dirt. I bet there's one with a little water down the hole.

When you clean everything up, use dialectric grease around the tip of the boot where it meets the plug, around the top where it seals to the COP, and around the seal area where the boot seals to the head.

 

Thanks for all the info guys. I'll pull all the COPs and check them too. I'm going tomorrow to get the stuff to clean everything out. Should I get a new gasket for the TB? Or are those reusable? One more question...Do you guys use the MAF cleaner spray to clean it or does something else work better?

 

I reuse the stock gasket. They are a hard board and should come off pretty easily without damaging the sealing surface.

Just about anything should do. I like mineral spirits on a rag, but wd40 or carb cleaner should work just as well. The scrubbing will be the only difference.

 

Yes the IAC can be cleaned (air flow inlet/outlet) and sometimes helps or cures the problem but there have been as many if not more times the IAC is defective and needs to be replaced.

The IAC is essentially a electrically controlled solenoid valve similar to a PCV (Pressure Control Valve not Positive Crankcase Vent) or TCV (Temperature Control Valve) which contains a diaphram. So, many times the IEC becomes defective because of a defective or worn solenoid or diaphram which is sealed and cannot be cleaned.

If cleaning does not help don't automatically assume it could be something else as the IAC could still be defective.

 

Krewat,
You mentioned water in the plug wells, is this a common problem? I only ask because I've got a buddy at work who recently bought a '97 150 with the 4.6 at auction. He had done new plugs and wires, and later (not sure how long, but couldn't have been too long) started getting a mis-fire. Hooked it up to my SCT x3 and got a #6 plug misfire. Pulled the boot and sure enough there was water (actually ice) down around the plug. Warmed it up, sucked it out with some hose and a wet-vac and everything was fine. But a little dielectric grease around the boot should stop it? Just curious if he should look for this to be an ongoing problem and how to prevent it.
Thanks
Sorry for the hi-jack

 

I went out today and got the MAF cleaner, TB cleaner, Di-Electric grease and Motorcraft Platinum plugs. Well I've got the TB and part of the intake with the MAF next to me here in the house. I'm going to clean them later when the wife and baby go to bed. When cleaning the MAF, you guys think just spraying the two little wires with the cleaner is good enough, or I've also read to clean them lightly with a Q-tip? I was also wondering if when everything is back together running Sea Foam thru the booster vac line would be a good idea too?

Upon removing a coil as suggested I noticed a lot of road salt and sand from the plow trucks around the coils. I left the coil off until I get my shop vac back tomorrow and can clean around everything. I'm going to get my long socket extension back also and try to do the plugs while everything is apart. Going to be 35 degrees tomorrow so it won't be too bad working on the truck.

One other thing....Is it definitely possible that this truck had no EGR? With the TB and intake off I still can't find it and I can pretty much see everything back to the firewall. I'm asking because if I'm just an idiot and don't see it, I was going to clean that as well.