1999 Mercedes E250 with P0171 and P0174 - No Vacuum Leaks Found, LTFT Shows 16% on Both Banks
I have a 1999 Mercedes-Benz E250 displaying fault codes P0171 and P0174. I've thoroughly checked for vacuum leaks and found none. During idle and acceleration, my Long-Term Fuel Trim (LTFT) readings show approximately 16% on both the lean and rich banks. The LTFT drops to near zero when accelerating but returns to 16% after I release the throttle. This behavior suggests a potential issue with fuel mixture regulation despite no detected vacuum leaks.
Perform a fuel pressure test. For vehicles showing P0171 and P0174, a common initial diagnosis is PCV system leaks or manifold issues.