rpm's raising slightly when breaking from acceleration ?
Thread Starter
Junior Member
Joined: Apr 2018
Posts: 36
Likes: 1
2008 s550 RWD
rpm's raising slightly when breaking from acceleration ?
Hey guys i have a question since we all have the same car it should be pretty easy for one of you guys to check it out and let me know. Today i noticed when i step on the brake after accelerating my rpms raise slightly for a second then lowers back to regular. This all happens when im driving i just need you guys to check while your going about 40-60 watch the rpms as you hit the brake to slow down and ldet me know if the raise a little before regulating.
Senior Member
Joined: Dec 2013
Posts: 314
Likes: 35
From: New York
2010 CL550
Hey guys i have a question since we all have the same car it should be pretty easy for one of you guys to check it out and let me know. Today i noticed when i step on the brake after accelerating my rpms raise slightly for a second then lowers back to regular. This all happens when im driving i just need you guys to check while your going about 40-60 watch the rpms as you hit the brake to slow down and ldet me know if the raise a little before regulating.
Thread Starter
Junior Member
Joined: Apr 2018
Posts: 36
Likes: 1
2008 s550 RWD
hey so mine is a 08 s550 base 103,000 i changed all 8 spark plugs already about two weeks ago so i doubt its the spark plugs it could possibly be the ignition coils but wont know until i swap them. during my research i saw it could also be a vacuum leak. im not really sure but it feels like how a manual car does when you downshift at higher speeds just not as noticeable. Like you i cant dont know if this always happened or just started 
Senior Member
Joined: Dec 2013
Posts: 314
Likes: 35
From: New York
2010 CL550
hey so mine is a 08 s550 base 103,000 i changed all 8 spark plugs already about two weeks ago so i doubt its the spark plugs it could possibly be the ignition coils but wont know until i swap them. during my research i saw it could also be a vacuum leak. im not really sure but it feels like how a manual car does when you downshift at higher speeds just not as noticeable. Like you i cant dont know if this always happened or just started
Thread Starter
Junior Member
Joined: Apr 2018
Posts: 36
Likes: 1
2008 s550 RWD
Yea i doubt its my air filters either i just changed them out a week before the spark plugs. It would be nice if other w221 owners could test it on there vehicle and chime in. In my head i want to say if your going fast and hit the brakes it makes the car downshift to a lower gear in turn raising the rpms for a moment then regulate after but this is a benz you would think it would throw it in a low enough gear to wear it wouldnt do that but hopefully more ppl comment and we can gather data
Super Member
Joined: Oct 2007
Posts: 643
Likes: 51
From: Southern California
2007 CL550
Could be simply a result of the transmission downshifting to lower gears as you slow down. When you shift to a lower gear, the RPMs must increase to match the current vehicle speed.
Senior Member
Joined: Dec 2013
Posts: 314
Likes: 35
From: New York
2010 CL550
if youve ever driven diesel trucks before, it feels like engine braking..which might be normal, but im not sure
