Good Morning All,

Looking for some input/help please. I've got a 2007 F150 FX4, 5.4 3V, with 70k miles. I've had a rough idle that I've been chasing for a couple months. Seems worst when AC/defrost is running, but I'm noticing it now slightly without AC as well, more so with warm engine sitting in drive than cold and/or in park. It's minimal, but noticeable, all the time though.

No CEL's. With all new OEM parts I've replaced spark plugs, COP's, air filter, fuel filter, MAF, Throttle body w/ TPS, run multiple bottles of techron through the tank, motorcraft oil filter and oil was just changed.

I started thinking maybe I had a bad plug or COP out of the box, so decided I'd get something to check mod$06 from the OBDII. Downloaded OBD Fusion app for my iphone and ordered an ELM32 wifi OBD adapter.

The app is working great (I'd recommend it for a $25 total investment), caused me to switch gears a little on the troubleshooting. mod$06 is showing (0) misfires. However, it is showing a failed test for $3C TID $81 EVAP MONITOR (0.020") failed. And that's the only one that hasn't passed.

Not sure if this is the source of my rough idle, but since it's broke I want to fix it. I've ordered a new gas cap since it's the easiest part to replace related to the evap loop from what I can tell.

However, my question for all the folks who know a lot more about this stuff than me. I passed the negative 0.020" pressure (TID $82) test, but not the positive pressure (TID $81) test. Is this an indication of which component in the loop is failing?

Thanks in advance for any responses!

 

just to throw it out there, I changed my coolant temperature sensors and it fixed my terrible idle my 89 had. Sometimes idle air control valve can cause a problem too

 

Thanks OleFord for the response! The idle control valve on the earlier gen 5.4's I believe was replaced by the throttle position sensor on the 3v's, so mine doesn't have one. Can't say I considered a coolant temp sensor, gauge reads ok on dash but I'll verify with the edge what temps the sensor is reading and go from there. Thanks again for the feedback.

 

Also thinking I could run through all of the steps performed during the positive and negative evap tests to see what each component is doing. But hoping someone can save me the work :-)

 

No need for an IAC when you have an electronic throttle.

There are 2 sensors - one for the temp gauge and the other for the PCM. It's also a head temp sensor, not a coolant temp sensor.

 

10-4, thanks for the clarification glc

 

Alright thanks for clearing it up. I'm just used to working on older stuff and I don't get around much of the newer ford trucks. Sounds like you've got a plan though.

 

A rough idle intermentedly was always a going coil for me. With no CEL I just change all of them. Try changing the PCV valve. Cleaning MAF and changing fuel filter is always a good idea.check vacuum hoses.

 

Thanks IntRiniTy for the feedback. I'm thinking the P0451 is unrelated to the rough idle, I changed the evap purge valve on the firewall and then the vent valve in the evap canister. Hoping one of those components was causing pressure build and the sensor to go out of whack.

The idle I've narrowed to only occurring from 575 - 625 ish RPM. Without AC when the idle drops in gear to 525 RPM it idles smooth.

I had already done all new motorcraft plugs, coils, and fuel filter (and a bunch of other stuff). Decided to check the new plugs last week and #7 looked a little suspect so I replaced it. Idles a bit smoother now that it's replaced, but can still feel just a little something. I've moved coils around and swapped in my old ones making no progress. Also switched to a Mobil gas station for a tank to see what happens. It's just about to the point where it's barely noticeable after the stupid amount of parts swapping I did, knock on wood. Since nothing made a drastic improvement, and it has been so incremental as I've gone, I think there was more than one issue and I'm just way too stinking picky for my own sanity and wallet.

 

The 5.4 3 valve doesn't have a PCV valve, it's a fixed orifice built into the valve cover.

 

Correct it's built into the valve cover.

I too have a check engine for evap control solenoid. Forget the code. I just keep turning it off. It's been months now no issues.

Worst case scenario- pay the $100 for ford to run a full diagnostic.

 

For what it's worth, even without a replaceable PCV, I still checked the fittings and insulated tube that run from the valve cover to the intake. Didn't discover anything interesting there. Used a propane torch to check the other vacuum hoses I could see and didn't notice a change in idle.

Against my better judgment I did take it into Ford, needed an inspection anyway, and had them check it out (it also had the pending P0451 at the time). Tech couldn't feel the rough idle, did a "decarb service" and flushed and filled the AC refrigerant because it tested low. Ignored the P0451 because I passed inspection with that test being the only one not ready. $600 later and no difference in idle, although I think the compressor is running longer and not short cycling, so the refrigerant replace didn't hurt.

I have a OBD to wifi adapter and an app that can pull live data of fuel trim and check mod $06 for misfires. What I found interesting was I pulled the wires to each COP briefly and plugged them back in. All cylinders but number 7 showed misfires, and wouldn't you know, cylinder 7 had what looked like a fouled plug. Doesn't make sense.

Anyway, thanks again guys for the feedback and if I ever identify a 100% smoking gun I'll circle back for anyone searching in the future!

 

Did you ever test the FTP sensor for skew or offset when at zero pressure (fuel cap off, engine off)? If not, you should. Neither valve can cause either that DTC. In any event, a small EVAP system issue will not cause misfires.

IIRC, on this era truck, the stored Mode$06 misfire counts (TID$80 & $81, sub-tests A2-AD) are not persistent across a PCM power cycle. You have to read them during the same PCM power-on cycle in which a potential misfire condition was perceived.

 

Thanks projectSHO89 for jumping in.

My app unfortunately doesn't have a PID for Fuel Tank Pressure, so actual root cause of the P0451 is completely lacking on my end. I monitored evap pressure and purge pressure and saw some funky values (shifts from -30 to +30 H2O), but I admit I don't fully understand the data. And had a heck of a time understanding where the FTP sensor is, and whether that OBD code relates to fuel tank pressure or evap pressure. Is the FTP sensor actually in the tank or in a fuel line? I used a scope above the fuel tank and only saw one place where wires run in, so I assumed those are just for the fuel pump. Once I couldn't find the FTP sensor I started thinking I was on the wrong track and that OBD code was for evap pressure.

I think that makes sense on a misfire monitor cycle. So you're saying although I started the truck, pulled the coil wires off each coil one after another, then shut the truck off (within 60 seconds or so) and checked Mod$06 right after shutting off the truck, that doesn't mean it would have caught the misfire on cylinder 7 but caught all others (because that cylinder was misfiring out of the cycle)?

Thanks for the education, I thrive on learning this stuff as a DIY'er and admittedly have a lot to learn!

 

For the misfire, go for a drive with everything hooked up and running, force it to misfire, usually by ******* it right after shifting into OD and going up a hill. Once you have felt the problem, pull over and read the misfire counts.

The FTP sensor is on the top of the tank where, ironically, it can measure the air pressure in the top of the fuel tank.