2001 C240 has OBDI code P0173
 

I tried to reset twice , the code of course comes back after 3 starts.
Freeze data indicates that it is always triggered at idle speed:

Eng speed RPM 725
Calc. Load 24.7
Map KPA 37
Coolant 183
ST FTRM1 % -2.2
LT FTRM1 % 17.9
ST FTRM2 % 0.0
LT FTRM2 % 19.5
ST FTRM3 % -100.6
LT FTRM3 % -100.6
ST FTRM4 % -100.6
LT FTRM4 % -100.6
Veh Speed 0
Fuel Sys1 CLSD
Fuel Sys2 CLSD

I think the problem is MAF sensor. Can somebody please confirm this, the MAF aint cheap so I wanted to be a bit more sure.

Thanks.

Looks like an air mass sensor, have you checked fuel pressure? 55psi regulated by filter?

I would think $225-250 for Bosch 0-280-217-515, would be a good price.

Thanks mbdoc, I have not checked the fuel pressure. I will, at 145k that fuel pump is certainly tired :)

I checked the pressure it seems to be not quite 55 but fluctuating and below 55, So I don't know if the pump or mass air sensor are causint the CEL?