Flickering battery light during idle
 

When the engine is idling the battery light mostly flickers. Sometimes it is ok.
I can make it do it by turning fan speed up/rear screen/lights on etc. If i rev the engine t he light disappears. I have had battery and alternator tested and both are ok. Voltages also ok during engine off/engine on. The only thing someone suggested was the engine was idling at too low speed, around 450 rpm. I can increase this idle speed by turning on the AC button which then increases the idle speed to around 550 ish, and the light disappears.
My question is how do i increase the idle engine speed without using AC button?

What are the numbers for the voltage readings? Sounds like the alternator isn't really good and it's weaker than it's made out to be.

Idle speed is controlled by the DME or as some people would call it the ECU. Perhaps you need a flash. It could also be something like not enough gas due to a fuel pump on the way out so there is less pressure in the line. A failing fuel pump may throw up a trouble light for a lean condition or not throw up any light. You can look at the long term and short term fuel trims.

Engine off right now is 12.1v
Engine on running idle is 13.8-14.0v (everything turned off)

replace batt

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Dirty/corroded grounds?

I would say your alternator is on its way out or your idle is low.

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My battery light started flickering after i changed my alternator eventually bad idling started. The problem was bad spark plugs and coils. Battery light stopped flickering after i changed the spark plugs and bad idling stopped after i changed the coils.

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Just had the same problem with my 2005 X5 3.0i and I went through the steps to diagnose it like others have posted. My 6 year old battery had low-ish voltage, and as this is my pregnant wife's car, I opted to start there and replace it. No success!

Next, I looked to the alternator and found the power steering reservoir leaking pretty significantly from the swollen rubber lines and dripping down into the alternator. Though the voltage while running was 13.5-13.9 (within spec) I know I've seen alternators fail intermittently in the past so I opted to just replace it. Again, it's my pregnant wife's commuter so better safe than sorry. As it turns out, this also did not solve the flickering battery light issue.

Finally, I searched on the forums and found several other stories that go: "new battery, new alternator, battery light still flickering". The resolution was a new ignition switch!

We last replaced our ignition switch in November 2015 around 120k with a genuine BMW part so I assumed that couldn't fail again so soon. I decided to throw in a $59 Febi switch (still made in Germany) and that has totally resolved the issue.

Here's a little video about my experience this week:

https://youtu.be/Rdo-IeK9HzY