fg2_matt

I have a bone stock 2012 Ecoboost Lariat 4x4 and it has a strange fluctuating idle that drops down to just under 500rpm and feels like its gonna stall. Vibrates the whole truck. Mostly when warmed up. It's sporadic, sometimes it does it sometimes it idles smooth. I'm going to change plugs and unhook battery to reset pcm. Not sure what else to try. has anyone experienced this? My old ecoboost idled around 600-700 rpm this one likes to stay right at 500.

Rougen123

Try the plugs first and report back

fg2_matt

So far I've done plugs (old plugs were from .034 to .045, new plugs gapped to .028), cleaned map sensors changed oil and trying to run out this tank of gas. I think it might be a tank of bad gas. I don't remember it idling rough on the test drive, and it was almost empty. Then the salesman filled it up and then it was idling rough. I have a little less than a quarter tank of gas in there now going to run it out as much as I can then put about 15 gallons of premium with a techron fuel system cleaner through it and hopefully that clears it up. If that doesn't work I'm not sure what else it could be.

Rougen123

You could try filling back up with premium . My truck idles kind of rough too. Idles around the rpm range you've mentioned - no issues for me. There's been times before I've replaced the plugs and I felt like it cleaned it up some - doesn't usually stay like that for long or it's just in my head. I've never cleaned my map sensors.

fg2_matt

Yeah if it's not bad gas I guess I'll have to just live with it. Runs great other than the inconsistent rough idle. A ford tech mentioned it might be worn out motor mount, which I find hard to believe at only 67k miles. They hooked it up to IDS and it showed no misfire.

fg2_matt

Well wasn't bad gas. Ran the old tank completely empty and filled up with shell 93 and ran a techron fuel treatment and still doing it. This thing is driving me nuts. Feels like its misfiring terribly but not codes.

jdunk54nl

How many miles on the truck? Where do you live? If it is a humid area then it might be sludge in the intercooler. Look up the f150 weep hole and try that. Usually it only happens under acceleration but could be an issue if it has a lot in it.

Also do you have any misfire events? If so it could be a bad COP on one of the plugs.

How is your battery? Weird things happen with bad batteries, especially at idle.

Any PCV leaks anywhere? Could also cause it to idle rough

fg2_matt

Truck has 67k miles. I live in Florida. Intercooler is clean. No misfire showing at all. Battery is fairly new. Has a UPR mega catch can installed recently and no change at all.

I'm at my wits end. The truck runs incredibly other than at idle, where it shakes the whole truck badly. Ford tells me its normal for these trucks but I know better as I had one before this and my father has one and neither of them have or have had this problem. I'm going to do a smoke test of the vacuum system, maybe a hose has a crack in it or a loose connection? Throttle body looks like it was replaced recently, so I tried to do an idle/throttle position relearn to no avail.

Stu Cazzo

My 2013 eco did exactly the same thing...it started idling rough and missing at idle.
No codes and this lasted about two months then the timing chain P0016 code came on.

New timing chain later it runs like a charm.

BareBonesXL

No warranty or you just want to keep it and think you got a good deal because it has a simple problem?