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

Do you have a detailed description of the codes? Also, some manufacturers list what parameters will trip the specific code, not sure if MB has this or not.

An example would be:

To set code P0 abcd, "engine coolant temp sensor low / open", the following must occur, Engine running for 10 minutes, sensor value below 50 * F.

Cause is most likely a small vacuum leak coming from some where.

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

How long has it had the k&n filters on it?

How clean is the throttle butterfly?

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Jim

K&N's were installed after the code came on.

I haven't inspected the TB.

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

Open the TB and try to see how nasty it is in there. I find it easy to remove to clean it and this allows you to look around a little closer. Use caution spraying in the area where the rod goes through the housing.

Have you sprayed carb cleaner or something like that all around the intake area while the car is sitting there at idle? When you hit the area where it is leaking it will increase idle slightly.

Do adaptation after cleaning.

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Jim

Reusable K&N filters are known to throw oil which will foul the MAF. If you haven't done so, try cleaning the MAF with C&R MAF cleaner. Note - Insert must be removed to spray on sensor. Fasteners are usually Torx Plus (5 point).

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Good luck.






1998 E320 Wagon

I cleaned the TB, it wasn't very clean but not out of the norm. I avoid spaying flammable fluids on running or hot engines (set a porsche on fire once from doing that). I wish I had a smoke machine but they are a bit to pricey for me.

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

The K&N and Mass air flow are only a few days old along with the other items I listed.

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

while replacing as many vacuum lines as I can find I came across the vacuum switch for the EGR and was wondering if this valve of some sort is broken or does it normally have this type of look. I'm guessing its some type of 1 way valve/filter, I can't see where it would plug in to or maybe there was an outside cap that should be attached to the end. Does this part look normal to you?

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

Looks like it may be missing a screen piece. That would be easy enough to test. You got a Mity Vac?

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Jim

I figured out what this part is thats attached to the Exhaust Gas Recirculation Vacuum Transducer:
ATM Atmospheric pressure, air admission via cylinder head

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

Take a look at throttle opening percentage / voltage at idle.

If the numbers are low, it points towards a vacuum leak post throttle body because the throttle is closing to maintain idle speed. A failing brake booster can cause a vacuum leak also.

If the throttle numbers are normal and MAF low, you have air entering between the MAF and throttle body ( maybe from the crank case breather through a oil cap / dipstick o ring ).

Great tip, I didn't think of that.

I replaced the TB to Elbow rubber seal and reset the mixture adaption. So far 90 miles with out the code coming back on, all monitors are ready except for the cat and evap, I've tried to complete the drive cycle twice.

The old seal was starting to get hard and would crack a bit when you bend it.

Hopefully I'm good to go. Thanks for the help.

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

After 300 miles the codes have came back on.

I noticed my intake manifold pressure sensor is reading 318 hpa at idle which I believe should be a negitive number, when the engine is reved the number doesn't drop below 200s. Maybe I'll try swapping pressure sensors. What is your IPS reading at idle?

For future search purposes my iPad scanner shows these codes as P0170 & P0173 where as my sds shows P0171 & p0174

Also to add to the parts replaced list is:
#6 OE maf rubber seal and TB rubber seal

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