Help me with a diagnosis!

HyeWarrior · 07-11-2018, 06:52 PM

DCT N55 with almost 80k miles

I was out running errands today when I noticed my idle was slightly fluctuating and irregular lurching (which I've known to be common with DCT cars). I was running AC (which I rarely do). I also noticed that on one of my starts, the car seemed to hiccup a bit to get going (I've already replaced the starter and alternator in the last 10k miles). I assumed it might be due to my fuel since I just switched from Shell to Chevron this week. I had a similar problem a while ago when I was running Costco gas, switched to Shell and problem was solved, so I thought maybe the sudden change in fuel was causing some hiccups.

Anyways. On the highway, car gets a half check engine light and goes into limp mode. Pull over, take the key out, restart, all seems well. Got the car home under cautious driving. With the car in idle, it seemed fine. Then I started to play with the AC a bit. Now I know its normal for the AC to cause some slight fluctuations. Though, when I put the AC on Auto, leave it for a little while, and then shut it off, the whole car seems to stutter almost like a misfire and nearly go into limp mode again.

Initially I thought it may be the HPFP or a VANOS solenoid, but now I'm not so sure.

Hoping this thread can shed some light and maybe help some others too.

Thank y'all!

10" · 07-11-2018, 07:44 PM

Quote:

Originally Posted by HyeWarrior

DCT N55 with almost 80k miles

I was out running errands today when I noticed my idle was slightly fluctuating and irregular lurching (which I've known to be common with DCT cars). I was running AC (which I rarely do). I also noticed that on one of my starts, the car seemed to hiccup a bit to get going (I've already replaced the starter and alternator in the last 10k miles). I assumed it might be due to my fuel since I just switched from Shell to Chevron this week. I had a similar problem a while ago when I was running Costco gas, switched to Shell and problem was solved, so I thought maybe the sudden change in fuel was causing some hiccups.

Anyways. On the highway, car gets a half check engine light and goes into limp mode. Pull over, take the key out, restart, all seems well. Got the car home under cautious driving. With the car in idle, it seemed fine. Then I started to play with the AC a bit. Now I know its normal for the AC to cause some slight fluctuations. Though, when I put the AC on Auto, leave it for a little while, and then shut it off, the whole car seems to stutter almost like a misfire and nearly go into limp mode again.

Initially I thought it may be the HPFP or a VANOS solenoid, but now I'm not so sure.

Hoping this thread can shed some light and maybe help some others too.

Thank y'all!

Sounds like a bad coil pack

02Pilot · 07-11-2018, 07:51 PM

You can guess, or you can scan the fault codes and save yourself the uncertainty.

That said, according to a BMW master tech I spoke with, the more-or-less definitive coil pack test is to drive at ~30mph in 6th and floor it. If there's a bad coil, this will expose it.

The Wind Breezes · 07-11-2018, 08:05 PM

If there's a bad coil it will show up on any scanner, even generic OBD2 scanners. In the year 2018 how does someone with over 800 posts on a car forum not have a scanner?

tracer bullet · 07-11-2018, 08:07 PM

Quote:

Originally Posted by 02Pilot

You can guess, or you can scan the fault codes and save yourself the uncertainty.

That said, according to a BMW master tech I spoke with, the more-or-less definitive coil pack test is to drive at ~30mph in 6th and floor it. If there's a bad coil, this will expose it.

Interesting technique, I will have to try it as well, I get a rough idle after startup and wonder if this is my issue as well.

I'm used to pulling codes after I see a CEL, but haven't seen one.

02Pilot · 07-11-2018, 08:44 PM

Again according to the aforementioned BMW master tech, coil problems may be quick, transient, and infrequent enough not to set a CEL/SES or fault code, especially early in the failure process. The technique I mentioned may or may not cause a fault to be set, but it should give you a sense of whether you're barking up the right tree.

Cpt.K · 07-12-2018, 02:28 AM

I had identical symptoms. Started less frequent and only when driving it a bit "harder." Eventually got to pop up more consistent and ended up being one of the VANOS solenoids so I replaced both for good measure.

+1 on reading the codes. Even without CEL there may be pending codes or just scan before you take the key out next time it happens

Good luck

HyeWarrior · 07-13-2018, 01:06 PM

Thanks everyone for the input! And usually I leech off my brother in law's OBD reader but he's out of town lol. I should really just buy my own at this point

Slight update:

So it looks like it's an air intake issue. Might have a leak or tear somewhere. Mechanic will be doing an air compression test today.

guslealisla · 07-16-2018, 12:32 PM

That happened to mine as I pulled out of the dealership after buying my used 135 with 78k miles no warranty. Code said maf sensor. While replacing it I found the charge pipe blew off and disconnected from the throttle body. New one in the mail. I would check both charge pipe connections

07-11-2018, 06:52 PM	#1
HyeWarrior Major 747 Rep 1,119 Posts Drives: 2012 135i DCT Join Date: Aug 2010 Location: San Dimas, CA iTrader: (1)	Help me with a diagnosis! DCT N55 with almost 80k miles I was out running errands today when I noticed my idle was slightly fluctuating and irregular lurching (which I've known to be common with DCT cars). I was running AC (which I rarely do). I also noticed that on one of my starts, the car seemed to hiccup a bit to get going (I've already replaced the starter and alternator in the last 10k miles). I assumed it might be due to my fuel since I just switched from Shell to Chevron this week. I had a similar problem a while ago when I was running Costco gas, switched to Shell and problem was solved, so I thought maybe the sudden change in fuel was causing some hiccups. Anyways. On the highway, car gets a half check engine light and goes into limp mode. Pull over, take the key out, restart, all seems well. Got the car home under cautious driving. With the car in idle, it seemed fine. Then I started to play with the AC a bit. Now I know its normal for the AC to cause some slight fluctuations. Though, when I put the AC on Auto, leave it for a little while, and then shut it off, the whole car seems to stutter almost like a misfire and nearly go into limp mode again. Initially I thought it may be the HPFP or a VANOS solenoid, but now I'm not so sure. Hoping this thread can shed some light and maybe help some others too. Thank y'all!
	Appreciate 0 Tweet Quote

07-11-2018, 07:51 PM	#3
02Pilot Malcontent 188 Rep 305 Posts Drives: 128i Join Date: Jul 2017 Location: NY iTrader: (0)	You can guess, or you can scan the fault codes and save yourself the uncertainty. That said, according to a BMW master tech I spoke with, the more-or-less definitive coil pack test is to drive at ~30mph in 6th and floor it. If there's a bad coil, this will expose it. __________________ Life's tough. It's tougher when you're stupid. -John Wayne
	Appreciate 0 Quote

07-11-2018, 08:05 PM	#4
The Wind Breezes Lieutenant Colonel 912 Rep 1,850 Posts Drives: 135i N55 DCT Join Date: Apr 2015 Location: USA iTrader: (0)	If there's a bad coil it will show up on any scanner, even generic OBD2 scanners. In the year 2018 how does someone with over 800 posts on a car forum not have a scanner?
	Appreciate 2 Zombie_Head594.00 low1352210.50 Quote

07-11-2018, 08:44 PM	#6
02Pilot Malcontent 188 Rep 305 Posts Drives: 128i Join Date: Jul 2017 Location: NY iTrader: (0)	Again according to the aforementioned BMW master tech, coil problems may be quick, transient, and infrequent enough not to set a CEL/SES or fault code, especially early in the failure process. The technique I mentioned may or may not cause a fault to be set, but it should give you a sense of whether you're barking up the right tree. __________________ Life's tough. It's tougher when you're stupid. -John Wayne
	Appreciate 0 Quote

07-12-2018, 02:28 AM	#7
Cpt.K Private First Class 24 Rep 115 Posts Drives: E91, E82, F80, F85, F87 Join Date: Jun 2017 Location: Huntington Beach, CA iTrader: (1)	I had identical symptoms. Started less frequent and only when driving it a bit "harder." Eventually got to pop up more consistent and ended up being one of the VANOS solenoids so I replaced both for good measure. +1 on reading the codes. Even without CEL there may be pending codes or just scan before you take the key out next time it happens Good luck
	Appreciate 0 Quote

07-13-2018, 01:06 PM	#8
HyeWarrior Major 747 Rep 1,119 Posts Drives: 2012 135i DCT Join Date: Aug 2010 Location: San Dimas, CA iTrader: (1)	Thanks everyone for the input! And usually I leech off my brother in law's OBD reader but he's out of town lol. I should really just buy my own at this point Slight update: So it looks like it's an air intake issue. Might have a leak or tear somewhere. Mechanic will be doing an air compression test today.
	Appreciate 0 Quote

07-16-2018, 12:32 PM	#9
guslealisla Private 18 Rep 49 Posts Drives: 2011 135I MSport Vert Join Date: Jul 2018 Location: Arizona iTrader: (0)	That happened to mine as I pulled out of the dealership after buying my used 135 with 78k miles no warranty. Code said maf sensor. While replacing it I found the charge pipe blew off and disconnected from the throttle body. New one in the mail. I would check both charge pipe connections __________________ 2011 135I MSport Convertible DCT. PS1,FBO,JB4 W/BEF.
	Appreciate 0 Quote