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I have a 2008 BMW X5 3 liter. I was having issues with a

Customer Question
rough idle and when I...
I have a 2008 BMW X5 3 liter. I was having issues with a rough idle and when I disconnected the MAF it disappeared. However when I replaced the MAF the rough idle came right back?
JA: Finding the cause of a rough idle can be tough, but luckily with the right help...solvable. The mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so he can help you best.
Customer: Thats it
JA: Are you hoping to fix this yourself?
Customer: yes
JA: Great! What have you tried so far?
Customer: Replacing the MAF
JA: Is there anything else important you think the BMW Mechanic should know about your BMW?
Customer: no
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the BMW Mechanic about your situation and then connect you two.
Submitted: 1 year ago.Category: BMW
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Customer reply replied 1 year ago
I recently changed all 6 spark plugs as it was throwing misfire codes which have now been eliminated. Prior to that both belts broke and were replaced.
Answered in 19 minutes by:
5/28/2016
BMW Mechanic: Steve, BMW Expert replied 1 year ago
Steve
Steve, BMW Expert
Category: BMW
Satisfied Customers: 24,284
Experience: BMW Expert
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Hello and welcome,
My name is ***** ***** it will be my pleasure to assist you today.
Just to confirm
With the maf unplugged it runs well, with it plugged in it idles rough ?
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Customer reply replied 1 year ago
that is correct. I also just bought a new maf and installed it and it is running rough as well.
BMW Mechanic: Steve, BMW Expert replied 1 year ago

I will provide an honest answer. I trust this will be appreciated. Please remember that a low rating PUNISHES me for being honest and that I receive nothing for my time until a positive rating is clicked.

.

thank you for your attention to the rating requirement.

.

the problem is that the engine is running lean - too much air in the air/fuel mix. this is a very common cause of rough idle and since you've replaced the maf that has been eliminated as the cause.

.

the reason the engine runs better when the maf is unplugged is that the engine automatically richens the mixture when it loses the maf signal, and this covers up the lean issue.

.

the most common cause of an air leak would be a tear or rip in the intake boot or track, or possibly a failed crankcase ventilation system. Low fuel pressure orr bad o2 sensors could also cause lean running, but isn't very common to cause what you've described - you likely have a leak or failed crankcase vent system.

.

The definitive test for intake leaks is a smoke test where a smoke machine (kind of similar to a fog machine you would see at a concert or on Halloween) pumps the intake full of smoke and then the smoke reveals the leaks as it seeps out through any cracks or holes.

However, you can still check for leaks at home. To check for intake leaks, visually inspect the intake area for any cracked hoses/pipes. If you can't see anything, you can try this trick: spray a can of carb cleaner around the intake with the engine idling. If the idle changes, this indicates that the cleaner is entering the engine and you have localized the area of the leak. You can then inspect further.

The most common source of air leaks is from the rubber intake tubes between the air box, and the throttle.

.

to check for a bad crankcase vent valve remove the oil cap with the engine idling, if there is high suction or you hear gurgling noises, this confirms it.

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if all turns up negative the next step would be a live diagnostic which can read all inputs and outputs from the engine control in real time and identify what readings are out of spec leading to the lean running

.

Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle.

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BMW Mechanic: Steve, BMW Expert replied 1 year ago
if there are no additional questions please kindly CLICK ON a positive rating
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BMW Mechanic: Steve, BMW Expert replied 1 year ago

did you have additional questions that were not answered about your rough idle?

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