Raspy Sound on Start up?

hassan_hamdan

Specialist
Aug 1, 2017
74
Hey guys, so i wasnt to sure if this was normal or not, but everytime i start up my n54 135i (Bone stock atm), i get this lound raspy rattle in my exhaust. Only lasts for about a minuite or two until engine warms up, then its completely gone. To add more confusion to this all, if during the first warm up period i pump the breaks a few times I hear a rattle in the exhaust again. But again once the car is warm its completely gone. Anyone know why or whats going on? I drive it around and cool it down before shutting off and absolutely nothing!
 

Jeffman

Captain
Jan 7, 2017
1,388
I think this is the dreaded N54 wastegate rattle. I just heard it for the first time last week (62K miles). I made it go away with MHD options when flashing.
 

hassan_hamdan

Specialist
Aug 1, 2017
74
I honestly dont think so, its only on cold start ups, other than that I drive the car hard, raced a few and hoenstly I never hear it at all. which throws me off so much!
 

Bmwfixerguy1

Lieutenant
Jun 5, 2017
872
May be the exhaust flap in the factory muffler. It's gonna be pulled shut at idle on warm up. To get me heat in the exhaust an warm up o2s quicker. It is on the same vacuum circuit as the turbos and brake booster as well. I'd pop the line off the muffler and plug it and check again. You can pop it off under the hood right at the hard plastic pipe to the brake booster it's the tiny nipple with vacuum line coming off and disappears into the fire wall.
 

hassan_hamdan

Specialist
Aug 1, 2017
74
May be the exhaust flap in the factory muffler. It's gonna be pulled shut at idle on warm up. To get me heat in the exhaust an warm up o2s quicker. It is on the same vacuum circuit as the turbos and brake booster as well. I'd pop the line off the muffler and plug it and check again. You can pop it off under the hood right at the hard plastic pipe to the brake booster it's the tiny nipple with vacuum line coming off and disappears into the fire wall.
Ahhh makes sense! Im planing on doing exhaust work later on so ill leave it alone for now haha thanks for the clairity!
 

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