On my 02 S55 160k miles I've been trying to solve these codes. The p0171 and p0174 only gets set after an extended period of driving and only at an idle. I've found good reason to change the following parts which have not solved my problem:

1. OE Mass air flow
2. New k&n filters
3. OE fuel filter
4. Valve cover gaskets and pcv hoses
5. Right side diverter valve

I ordered new intake manifold gaskets to be installed tomorrow. Any other suggestions?
My sds shows all o2 sensors are working correctly.

Is there a common place the intake manifold may have a hair line crack?

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1999 SL500
2003 C32
2002 S55
2004 S430
2003 E320
2004 E500