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I have a 2011 325i with 64000 miles on the clock. Over the last week or so it has developed a rough idle where I can feel the car judder slightly and the rev needle bounces up and down slightly, then when I accelerate away I can feel a misfire and slight judder. But after 5 minutes of driving it settles down and runs smoothly. If I turn the car off and on again after its been running it will be fine unless I leave it for a good few hours. It has full BMW service history but is overdue by about 2000 miles. I have got it booked in for a service with BMW in 2 weeks time. I thought it might have been injectors, spark plugs, MAF sensor, coil packs or something bbut don't understand why the problem goes away after 5 minutes when the car is warm.

Has anyone got any ideas what this problem could be before I start throwing money at it.

Thanks, Gaz
 

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Many possibilities, what have you actually checked? Coils, plugs, injectors, oil leaks on electrical wiring, air intake valves etc, after checking those get codes read.
 

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I haven't actually checked anything yet. I was just trying to see if anyone has had a similar problem and got to the bottom of it. I have read other posts where people describe the same problem and after having codes read they end up changing injectors, spark plugs, maf sensor. o2 sensor and coils etc all with no success. I would have thought that if it was any of those then the misfire would be there all of the time and not just after the first start up and for the first 5 mins of driving?
 

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Since you mention the rev meter I would get CCV checked out for split hoses, it requires taking off the manifold so may aswell replace the injector seals while you at it. Check top of the engine for oil leaks particularly around sensors and wire harness. The coils can also be full of oil.
You should be able to get a CCV kit quite cheap
 

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Yes, it's the injectors.

Whilst the car is sat overnight they leak fuel onto the spark plugs. This causes the rough idle on cold start but after a few minutes it's burnt off and all is well. If you inspect the plugs you'll find that one or more are blackened.

How do I know?

It's a very common and we'll documented problem on the N53. I have a 2011 E92 325i and mine did it at 50k miles which seems about right.

Good news is that the latest index 11 injectors seem to be proving much more reliable. The bad news is that the only sure way to fix the problem is to replace all 6 which I'm afraid is very expensive.
 

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+1

Pull your plugs after an overnight stop and inspect. Any pulgs that are black, wet and smelling of fuel will point to a failed injector.
 
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