Idle problems driving me nuts!
 

First off, Thanks in advance...I've spent hours and hours searching not only this forum, but other bmw forums and even as desperate as googling. I could find hundreds of people w/ similar problems but no particular fix.

I've got a 2006 4.4i w/ 61k miles on it. I bought it in june w/ 54 miles. It quickly developed a low rough idle that would studder under acceleration from a stop. I replaced the MAF and that solved the studdering and problems under acceleration.

But the idle is very rough and shakes the whole cabin. It happens in drive at a stop, in park, reverse and neutral. Once under way it seems fine, no sputtering or any noticeable problems. When the A/C is (no matter how low) the idle increases by about 100 rpm or so and the vibrations get MUCH better. Turn the ac off and it immediately drops back down to about 525 rpm. I've also noticed that I can give it a hint of gas to bring the rpms up by about 75-100 and it's much much smoother... this fix works in park, drive, whatever.

So in the past month or so I've replaced the MAF, replaced the air filter, changed engine oil and filter, ran several fuel system cleaners, always use chevron or shell 91....

Any ideas as to what else it could be ? is 525 rpm too low ? It seems to me it is simply idling too low per the computer.

How do I check for a bad engine mount(s) ? I don't think this is the problem though because a few rpm increase and the problem goes away ... can anyone advise ?

Spark plugs and fuel filter... I was going to change, but upon further research it is quite unlikely the plugs went bad at 55k miles. The fuel filter likely isn't the culprit at this mileage and if it was plugged it's effects would be felt on fuel throttle and higher fuel demands, which is not the case.

I've checked all the hose I can and don't see where there could be a vacuum leak...

The battery also seems to be in tip top shape and is an OEM bmw battery that looks like it is new.

I'm at a loss and it's getting really frustrating... any advice or insight from people with similar problems is much appreciated. I've found many incidents of similar problems but no culprit.

I am so glad someone else is as frustrated as I am with this problem. I have a 2006 4.8is with 54k miles. Hopefully someone can help us out.

You know man, I have the same model and now at 82K miles... my car has a little rough idle but nothing as worse as you are saying and it just drives rough.. Mine is a CPO and BMW techs have checked it out many times and they say - this is normal for E53 blah blah and they are loud and rough to drive and idle... So i am at a loss as well. I test drove an E70 and whoa loved that baby, unfortunately still too expensive for my wallet. Good luck finding the root cause

This is exactly why I have not taken in to a tech! I've read about everyone's experience w/ tech's telling them it's normal, if it doesn't throw a code it's ok, etc. It's definitely not ok and it makes my damn feet and legs irritated when I'm stopped in traffic or at red lights... I sure hope someone can help me because i really enjoy the combination of utility and handling of this thing... but I am not trying to replace engine mounts, spark plugs, battery, etc trying to chase down a solution.

Very good Drew,
Do not start chasing the problem because it won't solve anything. There are a lot of people on here; and I have done it myself, told the forum here, left and said "Damn, now I'm chasing a damn problem by throwing parts at it!"

Anyways, as far as the rough idle, it sounds like it has to do with the X breathing or emmissions. I would check to see the throttle body and look at that butterfly plate. If it is covered in carbon, that plate may have a hard time properly opening and closing. Carbon may be covering the plate, blocking air flow when the motor is in idle. If it is covered, hit it with throttle cleaner. I've done it on my X 4 times and no problems. You might trigger a CEL but it goes away after a few hours of driving. And emission wise, check the ERG valve a check to see if the valve is sticking, de to carbon build up. Anyone want to concur?

At least these things don't cost any money, well besides the $6 on the cleaner, and $9 for a 6 pack of bud???

Hey thanks, this is exactly the feedback and productive suggestions I was looking for! I forgot to mention I actually cleaned the throttle body 2 nights ago. It really really clean to begin with... The ERG valve I'm not familiar with. I'll have to look that up and check it immediately. Thanks a lot.

I had the same problem. Started using Techron - every other tankfull - no other service. Rough idle went away.

--2006 4.4i

I ran a tank full of techron followed by a tank of seafoam my last 2 tanks... and in total I've probably ran about 5 or 6 cleaners through... I'm not against throwing another one in there if it fixed yours. You had the same problem where the ac would fix the rough idle as well ? Am I crazy thinking the idle at 525 is just too low ? Thanks.

It appears only the 3.0D has the EGR... are you referring to something else I should check/clean ? Thanks

UHG you're right, I'm having another brain fart, its not an EGR system... I'm trying to find it on the diagrams what I am talking about. Ill get back to you.