The Unofficial BMW M5 Messageboard (m5board.com) - View Single Post

KevinM · 19th August 2007, 08:57

Well, from reading posts on this board for 3 years, here are my thoughts on what affects E39 M5 performance without other symptoms (rough idle, etc.), some of which you have already addressed:

1. Pre-cat O2 sensors
2. Plugs
3. MAFS
4. Air filters
5. Altitude
6. Hot weather

Although I may be mistaken, CPS failures usually cause symptoms.

Other members have reported subjective power gains by replacing O2 sensors before any codes are thrown.

I must say, however, that your car seems at bit young for many of these things. At over 50K miles, I have replaced one O2 sensor (code, no performance issues) but am still using the other original O2 sensors, CPS, and MAFS. I am considering replacing them as a prophylactic measure, but have not done so as the car is running great.

How about altitude issues (as compared to where you picked up the car) or heat?

19th August 2007, 08:57	#8 (permalink)
KevinM m5board.comoholic (>1000 posts) Join Date: Sep 2004 Location: Tucson, AZ Posts: 1,356 Thanks: 30 Thanked 30 Times in 22 Posts	Well, from reading posts on this board for 3 years, here are my thoughts on what affects E39 M5 performance without other symptoms (rough idle, etc.), some of which you have already addressed: 1. Pre-cat O2 sensors 2. Plugs 3. MAFS 4. Air filters 5. Altitude 6. Hot weather Although I may be mistaken, CPS failures usually cause symptoms. Other members have reported subjective power gains by replacing O2 sensors before any codes are thrown. I must say, however, that your car seems at bit young for many of these things. At over 50K miles, I have replaced one O2 sensor (code, no performance issues) but am still using the other original O2 sensors, CPS, and MAFS. I am considering replacing them as a prophylactic measure, but have not done so as the car is running great. How about altitude issues (as compared to where you picked up the car) or heat? __________________ Kevin 2002 M5, Sterling Gray/Caramel 2007 M Coupe, Silver/Black 1999 Mercedes ML320 (hauler...)