Rough Idle Update

[Hawk1339]

I had the same problem, and went through the same steps you did. When I closed the hood the rough idle would get worse. Turns out it was the clamp/grommet on the end of the air intake tube coming out of the MAF. The grommet wasn't slid over the plastic tube enough and when I tightened the clamp it created a gap that allowed air in. It was underneath so I could not see it happening. I thought about checking it after a trip to a u-pull-it salvage yard and running across a similar issue there.

I had the same problem. The end of the air tube fits inside of a groove in the grommet, but wasn't in there. The entire grommet was just over the end of the tube. Either it was that way from the factory or something I did in the past, I have had that off before. The air tube was distorted from being connected like that, so I hit it with a heat gun and molded it back into shape. With the grommet on correctly the leak is sealed and the occasional stumble I had seems to be gone.

One note on the stumble- it seemed to occur more when making a sharp right turn. I think the engine was shifting slightly from the centrifugal force and was opening the gap in the improperly fitted air duct.

 

[Blackedge03]

I had the same problem. The end of the air tube fits inside of a groove in the grommet, but wasn't in there. The entire grommet was just over the end of the tube. Either it was that way from the factory or something I did in the past, I have had that off before. The air tube was distorted from being connected like that, so I hit it with a heat gun and molded it back into shape. With the grommet on correctly the leak is sealed and the occasional stumble I had seems to be gone.

One note on the stumble- it seemed to occur more when making a sharp right turn. I think the engine was shifting slightly from the centrifugal force and was opening the gap in the improperly fitted air duct.

I checked it out but I don't see a grommet. I'm thinking it is not the same setup. The tube just slides over the outside diameter of the the mass airflow assembly and tightens down with a clamp. Same thing at the throttle body. But thanks for pointing it out.

 

[Blackedge03]

On thinking about the ECT some more I can't see how it would give lean burn. It can cause warm engine to run rich but I doubt there is enough range to go the other way. You can check it in the vehicle but I wouldn't drain the rad and remove it, I just don't think that's going to be the problem.

Ask your mechanic if the engine has a barometric sensor. It adjusts mixture depending on air pressure. I think it could cause lean burn - if that is the cause of the rough idle.

I can't find any info on the location of the map/baro sensor. O'reillys shows a map sensor for my truck but no price. Going to check out ebay for one . Checked the ECT resistance. Used some readings from fordfuelinjection.com
Don't think it the problem.When I unplugged it the CEL came on.
I have decided against taking it to the mechanic. He doesn't seem that interested anyway. I might take it to a different dealership if I can't figure it out. Not sure yet what I am going to do. At least it gets me to work and back even though I don't like it when I am sitting at a light, etc.

 

[Blackedge03]

I remember the tech advisor saying the truck was lean and mentioning something about the baro readings. They kept saying the reading was bad from the MAF sensor. Seems like if the baro reading was off it would point more to the MAP sensor or does the MAF control that?

 

[Rearanger]

My FSM says barometric sensor unique to supercharged engine. I guess the MAP does that job as well as denser air will cool it faster as will cooler air, so in the end it is the same thing. It's odd that you have no codes, but if lean only in idle I guess there may not be enough time for computer to read??? I can remember a problem I had with a Toyota when the rubber intake tube became loose, the car really ran rough at idle but no other time. Are you sure there is no slight leak in the intake tube, maybe from a small crack.

Of course MAP above should have been MAF

 

[Blackedge03]

My FSM says barometric sensor unique to supercharged engine. I guess the MAP does that job as well as denser air will cool it faster as will cooler air, so in the end it is the same thing. It's odd that you have no codes, but if lean only in idle I guess there may not be enough time for computer to read??? I can remember a problem I had with a Toyota when the rubber intake tube became loose, the car really ran rough at idle but no other time. Are you sure there is no slight leak in the intake tube, maybe from a small crack.

What I don't understand is there is a hose running from the left valve cover(looking from front of engine) to the intake tube where the IAT would go on earlier models. If I unplug it from the intake tube the idle doesn't change. Given this, it seems like I could cut a hole in the tube and it wouldn"t matter because there is a hole there when I unplug this line. Am I thinking wrong on this? I thought if I unplugged this line it should affect the idle due to there being a hole there. I am missing something here but I don't know what. I am tired of thinking about it...lol

 

[Rearanger]

If I unplug it from the intake tube the idle doesn't change.

Well since our engine and year are identical I went out and pulled that tube out of the intake (from top of valve cover to intake tube). There was no change in idle; there wasn't even any vacuum pulling through the hole in the intake tube as I would have expected. I checked and the hole goes through. The tube is to relieve any pressure in upper engine but it must only work when thottle is depressed. I guess there is more than ample idle flow through the MAF intake and IAC to negate any minor vacuum draw through the intake tube. So how much of a vacuum leak would you need to create a problem?

 

[Blackedge03]

The first time I pulled that tube out I expected to feel a vacuum there as well. Another thing that is confusing me is the Tech advisor at the dealership said that sometimes people put in a new air filter and it doesn't seal off right and that can affect the idle.Today I unsnapped the top of my airbox and lifted it up like to change the filter while the engine was running and it didn't change the idle. Makes no sense to me. On the other hand ,maybe since the idle is already rough it wouldn't make a difference.
Also, I put in a new purolator filter when I bought the truck but it was idleing
rough with the motorcraft that was in there.
I thought from past experience and from some of the previous posts on here
that from the airbox to the throttle body had to be pretty much airtight. So I
don't know what to think. I am wondering what would happen if I took the intake tube off the throttle body while the truck is running. Would that be enough to change the idle?

 

[Blossom2]

Thanks,gave it a try just now. Idle did not change at all but no CEL.I don't understand why.The truck actually idles worse than when I took it in this morning. $85 for this!!!

 

[Hawk1339]

I checked it out but I don't see a grommet. I'm thinking it is not the same setup. The tube just slides over the outside diameter of the the mass airflow assembly and tightens down with a clamp. Same thing at the throttle body. But thanks for pointing it out.

It may not be the same, mine is a 93. There are large rubber grommets at both ends of the air duct, the same diameter as the duct ends. They have protrusions on them that match notches in the clamps to prevent the clamps from creeping. The ends of the duct fit inside deep (~1/2") grooves in the grommet to form a tight seal against the MAF and intake.

 

[Blackedge03]

Well since our engine and year are identical I went out and pulled that tube out of the intake (from top of valve cover to intake tube). There was no change in idle; there wasn't even any vacuum pulling through the hole in the intake tube as I would have expected. I checked and the hole goes through. The tube is to relieve any pressure in upper engine but it must only work when thottle is depressed. I guess there is more than ample idle flow through the MAF intake and IAC to negate any minor vacuum draw through the intake tube. So how much of a vacuum leak would you need to create a problem?

Pulled the intake tube off the throttle body with the engine running and the engine died, so I guess that answers that. This thing must be sucking air somewhere else. Almost ready to throw in the towel.

 

[SixFoFalcon]

First off, the "mechanic" who told you that crap about the air filter not sealing is full of it, so you should ignore pretty much anything else they told you. You can throw the air filter 10 feet away from the truck and the engine will run just fine. Of course you'll be letting dirty air into the engine so that's not a good idea, but it won't immediately make the engine stall or idle funny or anything like that.

The crankcase breather tube never sees any appreciable vacuum at idle. It's just a vent for the crankcase so that whenever there is too much or too little pressure, there is a place for air to come or go from the system. In other words, if the PCV is only sucking out half of the blowby gases that are getting into the crankcase, the breather lets the other half escape rather than letting pressure build up; and conversely if there isn't much blowby happening, and the PCV is sucking too hard (huh-huh, huh-huh), the breather allows some air to enter the crankcase so it doesn't end up under vacuum.

The fact that that hose leads back to the intake is irrelevant--since it's upstream from the TB, it never sees any manifold vacuum anyway. The only reason it's stuck in the intake tract at all is so that any gases that are coming out, get dumped back into the engine rather than vented into the atmosphere; and conversely any air that's being drawn the other direction (into the crankcase) has to come in through the air filter and thus won't contaminate the oil.

 

[SixFoFalcon]

When you removed the air intake tube from the TB, you introduced unmetered air. In other words, normally there is nowhere for air to enter the intake without passing through the MAF sensor. So the PCM can use the readings from the MAF to figure out how much air is getting in, and it can add the appropriate amount of fuel to match. When you let air sneak in without checking in with the MAF, then the engine doesn't know how much fuel to add. This isn't a vacuum leak... it is occurring upstream from the TB. Just like removing the breather tube isn't a vacuum leak.

 

[SixFoFalcon]

Sorry for all the responses, but I'm reading back through the posts in this thread and your previous one to see what has and has not been done.

Have you done a fuel pressure test? How about a compression test?

 

[Savage Rules]

Hey I don't if this will help.
I've got an '08 with 8500kms with the same problem
Dealer replaced the plugs, wires, coil, PCM & now both heads (didn't fix the problem!).
Ford techs now believe that there was water in the fuel system.
They claim that there's no way for fuel to get out of the fuel rail & as it burns off - the "stutter" occurs.
They say they missed it because... I had miss-fire on every cylinder but #1, later it cleared up & only affected #3 & #6.

I've put two tanks of fuel through it so far & I still get a rough idle (no engine light now) at 1500-2500 RPM... they now want to drop & drain the fuel tank.

I'm in Canada... I don't know if you have the same temperature swings where you're at.