High boost after cold start?
Thread Starter
Super Member
Joined: Jun 2015
Posts: 643
Likes: 92
From: Houston, TX
'15 C63S
High boost after cold start?
I've recently noticed something strange that happens with my car when I first drive off after a cold start. I've noticed that the boost gauge will climb up to about halfway even though I'm barely giving the engine any throttle. It'll do this until I come to the first stop, and then after that it'll function normally. It does this in C, S, S+, and Race. It happens whether I'm accelerating normal or barely touching the throttle (<15 mph driving through my neighborhood). I thought maybe the gauge was just acting wonky, but I can hear the turbo spooling as it builds boost and then the diverter valve release pressure when the boost goes down.
Anyone else experience this? Is it normal? My car is a '15 that is stock and has had the ECU update.
Anyone else experience this? Is it normal? My car is a '15 that is stock and has had the ECU update.
Last edited by msd3075; Feb 14, 2019 at 11:15 AM.
Thread Starter
Super Member
Joined: Jun 2015
Posts: 643
Likes: 92
From: Houston, TX
'15 C63S
And I guess I should clarify what I mean by a "cold start". I'm not talking about the actual temperature as much as I'm talking about how long the car has sat between trips. It doesn't seem to matter the temperature of the engine. It'll do it when the engine oil is at 50F, and it'll do it when it's at 100F+. And at each of those temperatures it'll do it once and then stop.
Super Member
Joined: Sep 2014
Posts: 850
Likes: 111
From: NYC
18 E63S
It can go in ether direction and can be a combination of a bad boost actuator and bad vacuum hoses.
we can go back and forth on this or you can actually get it fixed Painlessly by taken it to the dealer.
Might also need a ECU update also.
plus there’s a campaign for replacement of all ignition coils
on 15- 16’s
good luck.
we can go back and forth on this or you can actually get it fixed Painlessly by taken it to the dealer.
Might also need a ECU update also.
plus there’s a campaign for replacement of all ignition coils
on 15- 16’s
good luck.
Last edited by tekfoc; Feb 14, 2019 at 04:29 PM.
Thread Starter
Super Member
Joined: Jun 2015
Posts: 643
Likes: 92
From: Houston, TX
'15 C63S
It can go in ether direction and can be a combination of a bad boost actuator and bad vacuum hoses.
we can go back and forth on this or you can actually get it fixed Painlessly by taken it to the dealer.
Might also need a ECU update also.
plus there’s a campaign for replacement of all ignition coils
on 15- 16’s
good luck.
we can go back and forth on this or you can actually get it fixed Painlessly by taken it to the dealer.
Might also need a ECU update also.
plus there’s a campaign for replacement of all ignition coils
on 15- 16’s
good luck.
Just got off the phone with the head mechanic at my dealer. Described the issue in detail to him, and he said every instance of kinked vacuum lines he's seen so far have resulted in low boost codes and significant loss in power. None have resulted in what I'm seeing. He said just to monitor it to see if it changes but that he highly doubts I'm experiencing the issue from the vacuum line TSB.
Thread Starter
Super Member
Joined: Jun 2015
Posts: 643
Likes: 92
From: Houston, TX
'15 C63S
