The lean mixture codes kept coming up on my S1 Roadster . I never did crack it. I did find the fibreglass was crcked on the air filter housing after the MAF sensor & repiared that. I replaced hoses all over. One was PCV vlavle to inlet hose. I bought a cheap one on ebay & it would collapse making a whistling sound on engine stop. Repelced by the original and it went away.
