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Hello Bimmer World! (this is my first post) I have 2008 528i and it has some issues I recently replaced the alternator along with the belt the belt tensioner and the mass air flow sensor the guy who helped me put it in said to reset the codes by disconnecting the battery and reconnecting it. I did that and since that it has been running worse than before.

1st. When in idle it revs the engine while my foot is in the brake in between 0 and 1000 revs then moves up toward the 1 mark.

2nd. My vents will be blowing cold air like normal then out of no where it will start blowing hot air out of the defrosters (front and rear) and I'm not able to control the ac/heater

3rd. The overheating caution message comes on and goes away after 1-2 minutes while driving.

Thank you very much in advance.
 

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Seems like you have air in the cooling system.
 

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Check the coolant level in the morning. If it's low, you have a coolant leak somewhere that causes having air in the cooling system. Once there is air present in the coolant passages in the engine, the heater core won't always get coolant since the heater core pipe comes from the top of the engine.
Also when the coolant temperature changes quickly up and down points toward having air in the system.
 

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One more possibility is that the water pump is acting up. If it's the water pump, it will throw error codes that can be read with a reader.
 

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The issue 1 is not related to issue 2 and 3.

throttle body, gas and brake pedals have multiple sensors that are compared to each other. if any of them is failing, will throw an error code that can be read with a code reader or INPA.
 
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