Hey all,

I am a new member to this site, but have been referencing it for quite some time anonymously. This weekend I decided to knock out some maintenence on my truck, '05 F150 4.6l, so I did a spark plug change on friday. I checked the gaps on the plugs, and did the change correctly (IMO obviously). Afterwards, I started the truck and didn't hear any misfiring, or anything crazy. I also drove the truck to the local parts store, and took the GF to sonic (a shake is well deserved after plug hunting on this motor!), with no problem. On saturday I changed the fuel filter. On my first run, I broke my line disconnect tool, and had to rehook my old fuel filter back up and ran back to the parts store to get another. On my way back, truck would idle and accelerate fine, but when coming to a stop at a light or stop sign, it would die. I managed to get it home, and change the fuel filter. After the new filter has been installed, the problem is still there. I turned the ignition on without starting it multiple times to rebuild my pressure. The truck will idle fine and when I apply the gas pedal, it will build RPM's fine, but as soon as I let off the accelerator, it will idle rocky for a minute, or bottom out and die. Thoughts?

 

Here is an update (as I took the day off to attempt to remedy this problem).

I have been reading through about anything I can find on the site and on the 'net. Have referenced my Haynes manual.

I disconnected my battery, turned my ignition to the on position, and reconnected the battery. Let it run for 15 mins as I have read the trucks computer may need to "relearn" the correct idle range. No change.

Then, after reading another post, I applied my brakes, and shifted through the gears. There was an extremely noticeable drop in RPM's when shifted from park -> drive or reverse. There was an extremely noticeable rise in RPM's when shifted back to park from one of these gears (loud enough the GF could tell the difference while sitting in her truck, which was running, while getting ready to go get some cope and beer for me).

I have yet to hit my local Autozone to get it scanned, although no Check Engine Lights are on (as it is lunchtime and traffic will be crazy - not good for a truck that is stalling at lights).

I do have a hypertech scanner at my house (at the GF's currently and my house is approx 30 min away) - would that be able to read my DTC's as efficiently as the scanner AZ would use? I've never installed the programmer, so I'm not familiar with it. Got it for $50 from a friend who traded in his truck, which was identical to mine.

I hope you guru's get on here soon, as it is too hot to stay outside and troubleshoot this (I live in North Carolina) and the GF would freak if she didn't get to watch "best dance crew" ... obviously this enviroment is inhospitable currently. Thanks.

 

I guess I will just continue to update this as I work IOT keep my information up to date as to help the smart people on the forum help me with my problem. Have read multiple posts about problems nearly similar to mine. Will start with the cheapest first, and will clean my throttle body up with a 3 dollar can of cleaner. If that doesn't work, I'll brave the stop lights & crazy traffic, and get my codes read at autozone.

 

What brand of plugs and filter did you use? Modular motors despise anything but Motorcraft parts.

Is the Hypertech a scanner or programmer?

 

I used motorcraft plugs, PN : sp-493 and a champion filter (as AZ did not have any motorcraft on hand) PN: FF686. I talked to a guy at autozone just now as I was buying some throttlebody cleaner, and he suggested it might be my torque converter, but I fail to see how simply installing a fuel filter would create a mechanical problem like that. I'm kind of under the impression that my computer has lost all the slowly gathered data on throttle body carbon build up and once I D/C'd the battery, data was lost, and my RPM's drop when returning to idle from acceleration. But I'm no mechanic obviously.

Hypertech is a programmer. But I seem to remember when I read the manual that it would identify DTC's. Maybe I'm wrong, I've been blown up a few times overseas and memory can be a bit selective haha.

Also, would a scanner even pick up a problem, if my truck isnt currently showing a CEL?

 

The computer doesn't learn anything, so disconnecting the battery didn't do anything. Hopefully some of the members with vast trouble shooting knowledge will chime in.

 

"Over a period of time, the PCM is able to automatically compensate for the slow loss of airflow past the throttle plates by either opening the idle air control (IAC) valve more (on cable actuated throttle) or by opening the throttle plate(s) wider (on Electronic Throttle) to increase airflow. When the PCM is reprogrammed, this learned setting is erased. On older vehicles it wasn't a very big problem because the learning curve for the idle was fairly quick and the vehicle could be back to normal speed in about 10 minutes. However, electronic throttle bodies have a much slower learning time which could take weeks or months to fully recover.

So, you have an electronic throttle vehicle. Now what do you do? Actually, there is a really simple fix: Clean the throttle body. In most cases, the throttle body is fairly easily accessible using only simple hand tools. Just remove the inlet tube assembly to achieve access to the throttle opening. Once there, take a shop towel or rag and wrap it around the end of a toothbrush or some other plastic handled device. DO NOT use a screwdriver as you can gouge the side of the throttle body and damage the bore. Apply a little Carb Cleaner or Lacquer Thinner to the towel, open the throttle plate and clean the throttle bore. You will also want to clean the edges of the throttle plate as there will be carbon buildup on there as well. Ideally you will want to remove the throttle body to perform a thorough cleaning, but the above steps should at least help improve your idle quality." - http://dygytalworld.ehost-services139.com/php/FAQs.html

I had just read that and some other posts talking about the truck learning to adjust its idle points and throttle body opening to combat carbon buildup, etc. Thats the post I had open in my browser. As I said, I'm no mechanic, hence I came here for help. Either way I appreciate your attention and responses. It is fairly important that I narrow this down quickly, as I am a Staff Sergeant in the Army, and I can't really "take days off" as I did today. Not as easy as calling in sick IOTtroubleshoot my vehicle.

 

Mine acts like that after i reprogram it. it will almost fall on its face when i stop. have you set it back to stock and driven it for a while? make sure all your wires/cop got seated back onto the plugs.

 

I have never used the hypertech to reprogram it. But will check the COP's now before I mess with cleaning the throttle body. When I did the plug job, some of the coils came out of the boot, and that does make a bit more sense to me than the TB issue. But when I initially drove it (although it was less than a 10 min drive roundtrip) after the plug job, it ran fine. Will recheck them though. Could improper gapping be an issue? I did check all of the gaps prior to installing the plugs, I'm just trying to run all the variables through my head. Seems as if the problem started the next day, after the fuel filter was changed. Thanks for everything so far. I've got the comp in the garage so I can tweak as I stay updated on your responses.

 

Tightened up all COP's, and made sure elec conn's were tight too. Yanked throttle body off and cleaned it (damn easy if you've never done it). I sprayed it out with the air compressor, just giving it a bit more time for the cleaner to evaporate before I put it back on and see how she runs.

 

I assume you took the air intake off to get to the plugs did you make sure to hook the maf and breather tube back up?

on top of your motor there is what looks like a tire stem on one of your fuel rails. If you push it in it will bleed of your gas i made a tool out of an old air chuck with a hose on it. that way you can hook it up and then turn the key on and it will pump fuel I doubt this is your problem

are you up in fayetville?

 

I actually didn't bother to take the air intake off, just went around it. I hooked the TB back on, put the air housing back on, and took a 15 minute spin around the neighborhood. Had a/c on for the first run, off for the second. Seems to run good now, RPM's don't bottom out while stopping or switching into gear. Seems like the TB clean did the job, but also haven't ran it for awhile on the highway yet (5 pm = crazy traffic). So hopefully, this will have been a 9 dollar fix, and not repulling plugs or something stupid like that.

Yeah I am in Fayetteville. I just now noticed your Lejune location

 

Awesome!