Markes

Hi! I'm getting a P0171 code on my 2002 c240 with 250k miles. The engine has been idling roughly lately, and sometimes even turns off when the car is stopped at a light, or the computer will rev the engine a little bit to keep the car from dying.

Also, when I'm revving above 3000 RPMs sometimes the engine just seems to sputter and stop responding, and the car will slowly lose speed. These issues started around 6 months ago, and completely disappeared until lately. Sometimes, restarting the car will temporarily solve the problem.

Any idea where to begin diagnosing? Other threads have had slightly different issues it seems.

samaritrey

Try unhooking the MAF and see if idle changes.
Could also be clogged fuel filter, Weak Fuel pump, oxygen sensors, clogged cats among other things.
How DIY are you?

Plutoe

Yep, the P0171-self adaption of mixture for R bank cylinders is at limit value-enrichment over permissible limit---assuming you have a copy of DAS there are six prescribed test to determine the fault source-stating simply at coolant sensor and ending with throttle valve actuator and accelerator pedal sensor!


If you don't have the diagnostics well your F----ed!!

Markes

Ok I finally got to fixing this thing. The car was getting worse to the point that sometimes it wouldn't even start, and it would constantly stall during idle. I checked the codes again and got a pending P0104 (and also a P0174) this time as well so I went ahead and replaced the MAF.

Now it starts and idles fine, and even drives but if I press the accelerator down more that 25% the engine knocks and loses power. If I keep it pressed at 25% it manages to get to 5000 RPM just fine but if I press any harder the engine just starts knocking and losing power. What I'm calling knocking is a popping sound coming from the engine.

I've also recently replaced the fuel filter (after the issue came up, needed to do it anyway) so it's unlikely to be that.

Probably unrelated, but there's also a hissing sound coming from the AC when I turn the car on.

Any ideas?

EDIT: Nevermind, not fixed, just happened to be working when I tried it. Looks like I did the MAF for nothing.

Markes

I'm semi DIY, I should be able to do most simple repairs.

After the MAF it looks like I should be checking for vacuum leaks and fuel pressure, right? Is there any guide for checking for vacuum leaks? How can I check for bad O2 sensors or clogged cats?

Markes

No diagnostics here Where can I get it online? Could you post more information about the diagnostics I should be doing?

Markes

OK I got a fuel pressure tester, hooked it up to the port on the passenger side and started the car.... 0 psi. I could be doing something wrong but it's so dead simple I don't know what it could be...

Markes

Just an update for anyone who comes across this in the future. The pressure tester I used was broken. Once I dealt with that I measured again and got 20ish PSI, so I went ahead and replaced the fuel pump. That fixed it!

XOKRBXO

Did anyone figure out the fix for this? P2453 first few days now P2453 and P2459. 2012 Mercedes GL350 Bluetech