Strange intermittent stumble. Only at idle.

RenaissanceMan · #1 08-24-2016, 02:52 PM

'06 X5 3.0. I've done some research on the board here to see if anyone else has experienced this but not seeing identical symptoms in the threads I've read. For the last few days, idle is rough after 1st start of the day and only occasionally when coming to a stop during normal driving. Driving at speed is still normal and smooth without a stumble so far. Feels like a bad coil when it does stumble on idle, but again this has been intermittent. I'm assuming if a coil was going bad it would do it at all rpm's, but I could be wrong. Not getting a check engine light, either. Under WOT still pulls strong. Any thoughts on what might be starting to die?

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thrillcat · #2 08-24-2016, 04:26 PM

Stumble as in stuttering, or is it surging? Mine very intermittently surges when I come to a stop, and if I throw it in neutral it stops. Methinks it may be the valve body...

RenaissanceMan · #3 08-24-2016, 04:40 PM

Quote:

Originally Posted by thrillcat

Stumble as in stuttering, or is it surging? Mine very intermittently surges when I come to a stop, and if I throw it in neutral it stops. Methinks it may be the valve body...

Stuttering for sure. This just started a few days ago. But the intermittent nature of it has me scratching my head.

Big "J" · #4 08-24-2016, 05:27 PM

If you're not getting any codes then start with the basic preventive maintenance items. Plugs, fuel filter, fuel injector cleaning, etc... See if any of those help.

upallnight · #5 08-24-2016, 09:32 PM

Get a scanner that you can monitor live data while you are driving and when the engine first starts up. Usually a vacuum leak is the cause for stumble on acceleration and stumble on deceleration. Monitoring the Long term and short term fuel trim will determine if you have a vacuum leak. A vacuum leak will show a short term fuel trim of + as the computer is trying to compensate for a lean condition.

RenaissanceMan · #6 08-24-2016, 11:21 PM

Quote:

Originally Posted by upallnight

Get a scanner that you can monitor live data while you are driving and when the engine first starts up. Usually a vacuum leak is the cause for stumble on acceleration and stumble on deceleration. Monitoring the Long term and short term fuel trim will determine if you have a vacuum leak. A vacuum leak will show a short term fuel trim of + as the computer is trying to compensate for a lean condition.

Great idea. I have both INPA and DIS/GT1. I'm assuming I could use one of those?

EDIT... Looks like INPA has exactly what I need for that! I'll do some monitoring with it in the morning...

upallnight · #7 08-25-2016, 07:38 AM

I use an App called Torque Pro (only $4.99) with either my Android phone or tablet to monitor live data. Much easier than a laptop in the car. I keep the bluetooth scanner with the car so if I get a check engine light when I am out driving I can use my phone to read the code and monitor live data.

RenaissanceMan · #8 09-07-2016, 10:38 PM

Quote:

Originally Posted by upallnight

I use an App called Torque Pro (only $4.99) with either my Android phone or tablet to monitor live data. Much easier than a laptop in the car. I keep the bluetooth scanner with the car so if I get a check engine light when I am out driving I can use my phone to read the code and monitor live data.

upallnight, thanks for the headsup on Torque Pro. I bought it and a bluetooth obd scanner and i've been monitoring for a little over a week.

the stumble on startup and idle is still intermittent. after cleaning the DISA valve the frequency of occurrence diminished some, but i'm still seeing the symptoms every couple of days.

still getting no check engine lights or fault codes. car still runs great. i've been monitoring short and long term fuel trims and i'm not seeing any indications of a big vacuum leak. bank 1 long term stays between 1.6 and 1.9 and bank 2 stays between 2.6 and 3.1. the short term fuel trims at idle look pretty normal, usually varying between positive and negative values that get closer to zero once the car sits for a minute at idle. at this point i'm assuming i must have some really small leak that is only rearing its head at certain temps? i've also been monitoring the o2 sensor voltages and all 4 stay between .1V and .9V at any given time.

a former bmw tech i know suggested doing the CCV and all related lines since it has never been done on my car and i'm approaching 140k on the clock. given that my line going to the dipstick tube is pretty oil-soaked, i figured it can't hurt to do this job, anyways. i am going to do the replacement this weekend and post back with the results. i'm hoping it takes care of the issue.

thanks again for the feedback-

Scott ZHP · #9 09-08-2016, 07:29 AM

Clean your idle control valve and inspect the lower intake boot elbow for cracks/leaks.

upallnight · #10 09-08-2016, 07:50 AM

Quote:

Originally Posted by Scott ZHP

Clean your idle control valve and inspect the lower intake boot elbow for cracks/leaks.

Idle air control valve is often overlooked as a problem because one does not see it directly, but over time it can be stuck due to dirt. It is easily removed and check. If it rattle loudly when shaken, than it is o.k.

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