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Upon start car idles low, flucuates up and down until driving for 10 minutes

In the morning when I start the car it idles rough, revving up and down from stable to almost dies from no gas but after 10 minutes of driving car runs fine
BMW 530i 5 speed with 150K miles

Year?

I’m no expert on BMWs but in other cars that’s very often related to a vacuum leak somewhere an/or the Idle Air Control Valve (IACV).
To test for vacuum leaks, one can often detect where they are by spraying a little starter fluid around vacuum hoses. If the idle steadies out briefly, you’re in the right area. Then look for cracked hoses in that area.
IACVs can often be cleaned with some air intake or carb cleaner. Very rarely they actually need replacing but they do get clogged up so don’t behave at idle. On most cars they come off pretty easily and can be cleaned on the bench.
If you’re not into fixing your own car, bring it to a mechanic that specializes in BMWs only. I’d stay away from the dealer. They’ll hose you for a lot more.

I agree with Remco, but I want to add that the problem could also be the result of a defective temperature sensor.