Ok I will plead stupid, but after days of searching theforum I’m still confused. My short term fuel trim is at 25% at Idle on bothbanks, when I unplug the MAF it drops to Zero. Is this a vacuum leak or a bad MAF?I have 124k miles; the codes are P0170 and P0173. I cleaned The MAF and stillget the same readings. I looked for Vacum leaks and haven't been able to find any. Any help will greatly be appreciated

 

P0170 = Fuel Trim Malfunction (Bank 1)
P0172 = System too Rich (Bank 1)

One question. Are those fuel trim readings fully warmed up closed loop or cold open loop with mixture enrichment?

Looks like your MAF is toast if those are engine hot readings.

A vacuum leak would lean your mixture.

 

Thanks! yes I drove for 30 minutes mixed, car was fully warmed up. I just checked it today after my ride to work, which is 45 min highway, still 25% at idle, around 13 at 2500 rpm and 11.7 at 1500 rpm. Long term was .8 and 1.8. I'm ordering a MAF right now. Do I have to get anything adjusted with my computer or can I just plug the new bosch unit in and clear my codes. Thank again your the man.

 

As long as you get the correct MAF it is plug & play.

One more question. Is your temperature gauge operating normally? The only other thing that could cause your condition is a failing temperature sender unit so the ECU thinks the engine is cold & enrichens mixture.

It can't be O2 sensors or you would get a code.

 

Yes temperature gauge is working fine; I changed thethermostat about a month ago. I will keep you posted once I get the new MAf.Thanks again

 

Put in new Bosch MAF I got from Importrc and I still have 25% Short term Fuel trim at Idle on both banks CL and pending codes of p0170 and P0173. I guess I will double check for vacuum leak. could it be anything else?

 

I have never looked, but is there an intake air temperature sensor on the C230? That fuel trim seems way out of line even if the platinum were blown clear off the MAF.

 

The IAT sensor is incorporated in the MAF.

P0170 = Fuel Trim Malfunction (Bank 1)
P0173 Fuel Trim Malfunction (Bank 2)

Have you cancelled the codes & taken a decent run with the car for the MAF to calibrate itself?

Are you absolutely sure that the airbox is clipped down tightly over the MAF at the rear. A loose airbox causes the MAF to hunt.

If the harness & plugs are in good condition fuel trim is affected by.

~ Air leaks in the inlet system
~ MAF
~ Upstream O2 sensors
~ engine temperature

In the worst possible scenario the ECU but I very much doubt that unless someone has been fiddling with it.

You might have O2 sensors cycling too slowly but no codes and both banks at the same time would seem unlikely.

 

After much searching I found a leak in one of my hoses that is under a plastic wire holder. I went by the dealer and order it today, the parts guy had to come out and take a picture of it with his Iphone it sits under a bunch of stuff and has a bend. $8 hose, Hopefully this takes care of the problem the hose will be in Monday I will update then. but I'm getting great gas mileage with my new MAF (trying to make myself feel better)

 

When we DIY we don't have the pleasure of trying things from the parts dept like a dealer does. I doubt that your MAF replacement has been a waste of time at your mileage.

 

++
my MAF crapped out at around 116k miles.