Vacuum leak problem?? P0173
 

I am getting error code P0173 and my dealer told me it might be a vacuum leak problem (haven't brought it in yet.) I am wondering what this is and if it is an easy fix. Does it have anything to do with the gas cap as I noticed that the bottom of the inside ring on my cap seemed wet when I removed it to fill up last week? I have a 2000 E430 4matic.

PO 173 = Fuel Trim Malfunction.
Take it to the dealer & let him scan it to get some more details.
Could be several problems. ;)
As you can see when you read these.
http://www.peachparts.com/shopforum/search.php?searchid=574601

P0173
 

Same problem different MB,99 SL, cracked vacuum hose below MAF on mine, rough idle, air intake seal between MAF and throttle actuator, about $ 10.00 worth of parts, I thought the MAF was bad but it was just the rubber seal, Hopefully that is all it is for you , I got off cheap.
Good luck

Dealer ran codes, picked up the p0170 to go along with the p0173. He also cleared them for me. Suggested it might be air/fuel filter/maf etc. Got five miles and CEL came back on. Going to bring it to my indie tomorrow. Praying its not MAF.

Hi, my 2001 C320 is getting a P0170 and P0173 at the same time. I also have rough idle. Can you tell me what the dealer told you about your car?

Thanks

It's MAF ... $500 down the drain.

Not necessarily, I bought a brand new unit in an MB box for about $200. off ebay and seems to work fine so far.

Would one believe that the sensors in MAFs could be similar and interchangable?

The answer to all such analysis is to monitor the adaptation values. The P017x codes are all for exceeding the adaptive capability of the two separate adaptation systems; partial load and CTP (closed throttle). By watching the values the type of problem can be surmized and the solution proven. A code that says the CTP adaptation is at the limit for correcting a lean condition (additive value at 1ms or above) is likely to be a vacuum leak.

A part load value of a multiplicative correction of 1.32 is usually a MAF. Substitution of any piece and a short drive after reseting adaptation to zero will verify the solution as adaptation of mE systems happens in a few miles.

For those with real diagnostic capability one can do it scientifically. Go to a search engine and find a Volumetric efficiency calculator (they were first devised for deciding which size Holley double pumper to put on your small block). Run the engine full throttle (under load) while monitoring MAF, rpm, and intake air temp (this is best accomplished on a dyno or with a graphing scanner see: http://www.autoenginuity.com/ ) The calculator will need rpm, maf (in proper units), cid (in proper units) and intake air temp (in proper units). The answer should be above 70% for most engines and above 80% for most 4 valve engines and as high as 100% or more for turbo or supercharged engines.

BTW: Volumetric efficiency calculations also will verify plugged cats and jumped cam timing.