Car stalls but not with MAF unplugged

sle39lvr · 10-16-2018, 11:00 PM

I had to replace the starter motor.

So these components came off:
MAF sensor (I cleaned with MAF sensor cleaner
Throttle body (I cleaned with MAF sensor cleaner)
Intake Manifold.
Few breather hoses

Now the car would start, but stalls right afterwards. No codes.

When I unplug MAF sensor, it holds idle, though rough.

Is this for sure a bad MAF sensor? Or this could be due to other vacuum leak created from above ?

Thanks in advance

Bufalo · 10-19-2018, 08:43 AM

Vacuum leak. That's a classic symptom. Engine is getting unmetered air from somewhere, and because the MAF is plugged in and providing (an incorrect) signal, the DME doesn't compensate with more fuel. I chased the same thing on my old X3 until I found a wrecked front crank seal.

nsjames · 10-19-2018, 12:17 PM

x a billion on vacuum leak.

Efthreeoh · 10-20-2018, 09:29 AM

I agree, there is a vacuum leak somewhere. There should be a SES light now too (for the missing MAF signal). The engine will idle without the MAF plugged in because the ECU is not getting a MAF signal and goes into a predetermined map to keep the engine running as best it can. Check for a PCV hose being cracked or broken (common problem when removing the intake), or you left a hose off the intake when reinstalling it. Or an intake manifold gasket didn't seat correctly and is leaking.

My 2 cents.

gT-BMW · 10-21-2018, 01:49 PM

Did you plug in the fuel tank vent valve that goes behind the throttle body?

sle39lvr · 10-21-2018, 04:48 PM

Thank you for who gave input.

I started taking things apart. Found out that the breather hose that plugs in to throttle body was unplugged.

So it was indeed a vacuum leak.

Phyrexia · 10-21-2018, 10:28 PM

Thanks for the update! Glad you got it going!

10-16-2018, 11:00 PM	#1
sle39lvr Captain 124 Rep 654 Posts Drives: 08 328i Join Date: Aug 2011 Location: United States iTrader: (3)	Car stalls but not with MAF unplugged I had to replace the starter motor. So these components came off: MAF sensor (I cleaned with MAF sensor cleaner Throttle body (I cleaned with MAF sensor cleaner) Intake Manifold. Few breather hoses Now the car would start, but stalls right afterwards. No codes. When I unplug MAF sensor, it holds idle, though rough. Is this for sure a bad MAF sensor? Or this could be due to other vacuum leak created from above ? Thanks in advance
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10-19-2018, 08:43 AM	#2
Bufalo Second Lieutenant 124 Rep 287 Posts Drives: 2009 328i Join Date: Dec 2011 Location: Harrisburg, PA iTrader: (1) Garage List 2017 BMW X3 35i [0.00] 2009 BMW 328i [0.00]	Vacuum leak. That's a classic symptom. Engine is getting unmetered air from somewhere, and because the MAF is plugged in and providing (an incorrect) signal, the DME doesn't compensate with more fuel. I chased the same thing on my old X3 until I found a wrecked front crank seal.
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10-19-2018, 12:17 PM	#3
nsjames Brigadier General 2440 Rep 4,331 Posts Drives: 08 328xi Touring Join Date: May 2017 Location: ohio iTrader: (0)	x a billion on vacuum leak.
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10-20-2018, 09:29 AM	#4
Efthreeoh General 17207 Rep 18,696 Posts Drives: The E90 + Z4 Coupe & Z3 R'ster Join Date: May 2012 Location: Virginia iTrader: (0)	I agree, there is a vacuum leak somewhere. There should be a SES light now too (for the missing MAF signal). The engine will idle without the MAF plugged in because the ECU is not getting a MAF signal and goes into a predetermined map to keep the engine running as best it can. Check for a PCV hose being cracked or broken (common problem when removing the intake), or you left a hose off the intake when reinstalling it. Or an intake manifold gasket didn't seat correctly and is leaking. My 2 cents. __________________ A manual transmission can be set to "comfort", "sport", and "track" modes simply by the technique and speed at which you shift it; it doesn't need "modes", modes are for manumatics that try to behave like a real 3-pedal manual transmission. If you can money-shift it, it's a manual transmission. "Yeah, but NO ONE puts an automatic trans shift knob on a manual transmission."
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10-21-2018, 01:49 PM	#5
gT-BMW Lieutenant 203 Rep 437 Posts Drives: 06' 325i 6spd Join Date: Jan 2018 Location: FL iTrader: (0) Garage List 2006 BMW 325i [0.00]	Did you plug in the fuel tank vent valve that goes behind the throttle body?
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10-21-2018, 04:48 PM	#6
sle39lvr Captain 124 Rep 654 Posts Drives: 08 328i Join Date: Aug 2011 Location: United States iTrader: (3)	Thank you for who gave input. I started taking things apart. Found out that the breather hose that plugs in to throttle body was unplugged. So it was indeed a vacuum leak.
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10-21-2018, 10:28 PM	#7
Phyrexia Resident Pedant 503 Rep 792 Posts Drives: '15 335i 8AT Join Date: Nov 2017 Location: Limbo iTrader: (1)	Thanks for the update! Glad you got it going!
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