Okay so I been trying get my car fixed I toke it to plenty of shops and they couldn't figure it out when I start the car in the cold it shuts off after like 3 seconds and it drops rpm from 1000 to like 400 rpm and jumps up and down and stall out only way to keep the engine on is if I rev it until the temperature gauge is the middle and I can drive off but as I drive off I hear a very loud exhaust and bad acceleration like on the highway it will usually take me 4 seconds to pick up to highway speed when turning highway but now it takes me a 10 seconds to pick to that speed and aggressive gas pedaling to get it to speed and I hear knocking noise by the intake of the engine any suggestion ?
My car has 18300 miles.
My car has an automatic transmission.
Although it's nearly impossible to diagnose a problem remotely, it appears you might have more than one issue going wrong with your 2004 BMW. The loud noise and lack of performance is a pretty good indicator of an exhaust system leak, perhaps in the manifold or before the catalytic converter. The cold starting issues is commonly caused by low fuel pressure; which can be caused by the cold weather, clogged fuel injectors or a dirty throttle body that simply needs to be cleaned of excessive carbon buildup. The best advice I can offer is to have a professional mobile mechanic complete a car is hard to start inspection for starters, so they can determine what some of the issues might be causing the issues you're having with the BMW.
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