I have 102K miles on my 98 ML320.
I experienced the P0170 and P0173 codes as diagnosed by the dealer last November. I replaced the MAF at that time with a new unit ordered online. ML ran fine until lately. I am again getting these same two codes.

Could the MAF have gone bad so fast ?

I didn't see any visible vacuum leaks.

Symptoms are 1) takes lots of cranking to start when cold, 2) occasional backfire (at intake) when cold, 3) seems llike lower than normal power, 4) mpg indicator readings are lower than normal.

I used the laptop OBD-II code checker, just shows these two codes with no pending codes. I copied some of the sensor readings from the screen called " current powertrain diagnostic data"

$04 load pct = 19 to 24
$05 ECT = 108 to 145
$06 SHRTFT1 = -14 to +1.5
$07 LONG1 = 35.2 steady
$08 SHRTFT2 = -11.9 to +3.9
$09 LONG2 = 35.2 steady
%OB MAP = 9.8 to 10.7
$OC RPM = 742 to 819
$OD VSS = 0
$OE SPARKADV = -18 to -9
$OF IAT = 64 to 68
$10 MAF = 0.583 to .778
$11 TP = 3.5 to 3.9
$12 AIR = OFF
$13 O2SLOC = SEE
$14 O2S11 SHRTFT11 = 0.095 to 0.765
$15 O2S12 SHRTFT12 = 0.500 to 0.825
$18 O2S21 SHRTFT21 = 0.095 to 0.760
$19 O2S22 SHRTFT22 = 0.515 to 0.830

From another screen called "on board monitoring test results for non-continously monitored systems", I copied the failures :
TID=$09 and CID's = $01, $06, S04, S02, S05, and $03

I'm not sure what to conclude from this.
Any suggestions before I order another MAF ?

Thanks, Alex

Many times the 'plastic air tube from the air mass sensor to the throttle body will leak the the rubber seal ring at the throttle body. Iwould make sure that seal is NEW first. MB number 112-141-18-80.

Also try cleaning the air mass sensor with a very soft tooth brush as there might be a carbon build-up on it.

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my mass air flow sendsor went twice in approimatly 6 months.
the part was covered the second time and replaced .but mb wanted to put the ml on their machine to make sure this was the problem. this was ok. that part must be defective. it is simple to replace but quite expensive.

Just out of curiosity, have the spark plugs, air filter and fuel filter been replaced on schedule?

Gilly

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Thanks for the replies.

I changed the o-ring seal at the back of the plenum.
The old one seemed a little compressed, but no major failure.
This did not solve the problem.

I changed the sparks plugs and installed a new air filter on 06/2003 at 86000 miles.

I experimented by disconnecting the battery to reset the computer code. After that it ran very poorly and improved over time to the usual poor state, and the CE light came back on.

I just had my smog check done on 02/2004 and it passed easily, so something happened all of a sudden.

I purchased my last mass air flow meter online, and I can't find the receipt (I'm usually good at keeping records) so it would be difficult to claim this is the true cause of the problem (downside on online purchases).

I might try the cleaning procedure.

those codes = maf sensor needs to be replaced.. I had two ML's with the same codes and after replacing the MAF Sensors the light went away =)