NTX 2006 F-150

Hi all, new to the forum and glad to see you all here. I tried a search for my issue in prior posts with no luck. I have 106K on my truck and have had it for 2 months, so I don't know it's history other than to say that the truck is clean as a whistle and whoever had it seemingly took pretty good care of it. I love my truck. As the title indicates, I have a mildly rough idle, more slight when cold, and a little more noticeable after warmup. Also it is slightly less when in gear, a little more so when in neutral. There is also a faster than what I'd consider normal idle when cold, somewhere around 1200-1300 rpm, and it goes down to around 700-800 rpm when warmed up. There are times when the engine idles perfectly, so I have ruled out a vacuum leak due to gaskets/hoses. This one seems more like a sensor or a control valve issue to me. This problem is not severe at all, but I am a maintenance tech by trade, and the problem is more of a burr under my ocd oriented saddle than anything else lol. The truck accelerates and cruises perfectly, it runs like a new truck, it's only the idle where it seems to be less than ideal. I have been shooting in the dark, trying different things, have replaced some parts in hopes of getting to the problem, but no luck so far. I have an OBD II diagnostic tool on it's way in the mail for my laptop and was wondering what the normal values for the various readings would be?
Sorry for the epic novel

Things I have done so far:
Replaced air filter
Replaced PCV valve
Sprayed all lines and fittings around the intake checking for vacuum leaks
Replaced plugs and cops
Replaced injector o rings and filter screens
Replaced MAF sensor
Replaced EGR valve
Cleaned throttle body (took it off to do this and it did help some)

Things I'm considering:
Oxygen sensors
EGR differential pressure sensor
Throttle body / TB motor / Throttle position sensor

I hate to just keep throwing parts at it, anyone have any suggestions?

Thanks in advance!

Craig

Marc D

Wow. I've been sucked into the "part by part repair" vortex many times before myself. First let me say the cold start idle @1200 to 1300 rpm is normal, in fact it's perfect.
On to the other issues. I have to assume you have had a check "engine light" on for most of these issues. If not check the cig. lighter/CEL fuse. This controls the CEL light on the dash. Once you have your computer program you can check for stored codes as long as you haven't cleared them by disconnecting the battery. If you did, they will return. :-)
The most likely culprit is your EGR pressure switch. If it's an aluminum one, it's the factory unit. If it's black plastic it probably has been replace already.
If the truck needs O2 sensors, you should have P0171 & P0174 codes. (lean codes)
The throttle positioner is common but not at only 106K miles. Cleaning is all you should need to do.

NTX 2006 F-150

Some of the stuff on been there done that list I saw as tune up about due anyway stuff. As for the rest of it, hey, what can I say? I got sucked in alright lol!

Is the EGR pressure switch the same as the EGR differential pressure sensor?

Marc D

Yes. They are usually connected with two vacuum lines and a (3 wire) electrical connection. Mark the vac lines before disassembly so they don't get crossed when you install the new one. Good luck.

NTX 2006 F-150

Welp, got the OBD II software loaded, hooked up to the truck and got some values.

I found it interesting that there were some differences in oxygen sensor readings between bank 1 and bank 2, but they do seem to be functioning ok.

From what I understand, a misfiring cylinder can cause differences like that, but I'm am by no means very knowledgeable on this stuff.

I had a suggestion that it could be an injector that might cause a reading imbalance like that. Does that make sense? How common is injector problems like that?

Marc D

Any time you are searching for the solution to the kind of engine activity you are experiencing, fuel must be accounted for as a major contender. Fuel injectors can be functioning but poorly. If they don't shut off cleanly and dribble the motor can surge. If they are clogged you run with a low firing cylinder. Other than an removing them and bench testing then there's not any way to confirm their operation other than bleed down. You should be able to test the impulse readings on each injector wire plug to be sure they are operating electronically

NTX 2006 F-150

Makes a lot of sense.

The imbalance causing one side to go slightly rich, just might be injector related after all because yesterday afternoon I put some Lucas injector cleaner in the tank, which is advertised to clean and lubricate the fuel system.

There was a very noticeable difference in how smoothly it ran today. I'd already serviced the injectors by replacing the screens and orings. Since it idled great at times and not so good at other times, and the cleaner seemed to help, my best redneck un-edumucated guess makes me think that it's more likely a sticking injector vs a clogged one.

Gonna plan on running it for a while with a few tanks of the cleaner to see what it does. What do you think, am I off base here?

Marc D

You can use fuel additives for a few tanks (full) but then I would hold off for about 3000 to 4000 miles to see if your symptoms return. These types of chemicals are hard on the injector nozzle tips and can do damage over time. I use it only once every oil change, even in my wifes newer car with only 45K miles.