Rough idle, IAC valve?

[JJMaine]

I have been working my way through all of the small issues and maintenance on my new to me 2011 XLT 4.0 and it has a bit of a rough idle and the truck shudders a bit at idle. I have a Motorcraft fuel filter on order and also a new donut gasket for the exhaust (limits leaking slightly) but I am wondering if the IAC may be the culprit? The reason I ask is because when starting cold (or relatively cold) about half the time the truck revs initially to 1500rpms before immediately coming down to 1100 but the other half of the time it revs over 2000rpm before falling back down. To my untrained ear, 1500 sounds normal but when it revs to 2000-2100 on start up it makes me cringe a little lol.

I have a read that the IAC is many times the fix for a rough idle on these trucks do you guys think that's my issue or any other ideas? Or is 2000rpm on start up normal and not connected to the rough idle? Thanks so much!

 

[JJMaine]

A couple things I forgot to mention. I picked up a new air filter and will install it tomorrow.

Previous owner said that the truck got new plugs and wires at 96k miles (102,000 now) and I will be checking to make sure that they are new or at least the plug wires that I can see appear to be new.

 

[Ashrev]

I too have a rough idle. I just replaced my IAC and idle sits at 900 rpm when warm which I believe is correct. The idle smoothed a little bit but is still lumpy. Spark plugs are new so I'm trying new plug wires tomorrow. If that doesn't solve it, a new coil pack will be next. I know they are all really old so have no problem updating.

 

[JJMaine]

A bad coil/misfire crossed my mind as well since it has happened to me on other cars but I thought I should have a check engine light if it were misfiring? I’m going to take a good long look under the hood tomorrow and see if I find anything obvious (probably not) and clean the MAF.

 

[JJMaine]

Im also trying to take my belt off to have a look at the harmonic balancer and the rest of the pulleys because I get a weird chirp/thump when I take off that is def. coming from under the hood. From what I can read, the harmonic balancer might cause a rough idle and might also explain the chirping. None of this prevents the truck from running and driving just fine but Id like to get to the bottom of it nonetheless.

What do you guys use to turn the tensioner? I have tried a 3/8” breaker bar and ratchet but they both hit the fan. The breaker bar would work but the box end is at the wrong angle to fit in the tensioner. Do I need a ratcheting breaker bar?

 

[SenorNoob]

My effectively 92 model 4.0 has a significantly higher starting rev like that when the outside temperature is cold. (Below about 40F) I always thought it was normal.

 

[JJMaine]

It may be normal to me it just sounds better when it only revs to 1500 on start up lol. I just wasnt sure if it was another symptom of whatever is causing my rough idle.

Sometimes it idles down to almost 500rpm when coming to a stop in drive (like at a red light). Not sure if thats a clue either? I’m going to go down the lost of usual suspects but trying to diagnose things and replacing things that need to be anyway (air filter, fuel filter etc.) before firing the parts cannon at it.

 

[JJMaine]

I cleaned the MAF sensor and that didn't seem to make much of a difference. Is there any good fuel injection cleaner that I can add to a tank of gas that will actually work? Seafoam?

My motto: If you can't fix it, wash it.

 

[SenorNoob]

I have used a regular ratchet on the belt tensioner. The drop to 500rpm at stop signs definitely sounds like a sticky IAC.

Ford Idle Air Control – IAC – Clean – Replace

I wouldn't just replace it. A cleaned Ford part is much better than most of the aftermarket stuff. Some of the cheaper ones don't even get the basic principle of operation right.

 

[JJMaine]

I couldn't get a ratchet to fit with the fan blades there but I can try again. I was going to pick up a serpentine tool at AutoZone today but not for $40!

I hadn't thought of cleaning it, I figured it was just a trash and replace kind of part. I'll check that out and see about cleaning mine, thanks!

 

[SenorNoob]

IDK if Autozone does it but Oreilly's has loaner tool for that. $32 deposit. All your money back when you get done.

 

[JJMaine]

I didn't think of that either. My local AutoZone will let you rent any tool off the shelf (within reason I'm sure). They have a loaner program as well with specific tools for that but they've let me rent stuff that wasn't a part of their loaner program and then when I return it I think they just add that to their loaner inventory. My long winded way of saying thanks for reminding me that that was an option.

 

[Ashrev]

With mine it is definitely a combination of things. Each thing I've done has improved the idle bit by bit. Replaced the IAC, cleaned the MAF and replaced the fuel filter (which looked like the original from the amount of gunk all over it - had to pry it out of the clip with a pry bar). Still getting the occasional hiccup but haven't replaced the plug wires yet - hoping that might be the last piece.

 

[JJMaine]

CEL came on today P0455 evap code. Maybe a vacuum leak like the EGR valve? I don't have any way to test for vacuum leaks other than spraying carb cleaner while the engine is running?

 

[JJMaine]

What is this part? It is passenger side bear the blower motor I think. I was trying to find a vacuum leak with a hose connected to propane and when I put the hose near this it makes a chirping sound but no rev increase? Is this my vacuum leak? I put the hose in behind where the green arrow is