98 C230 engine performance issue(s)
 

I've heard from a few that this is a common problem, but either it isn't, or I'm not searching for the right thing. My 98 C230 runs and drives fine; as long as your foot isn't on the floor. When you floor the accelerator, the engine RPM climbs, but accelerates slowly. (This is not a slipping transmission feeling; more like power loss/bogging) Let off the throttle a bit, and it upshifts and accelerates smoothly. It's quite odd, and this happens at any speed, whether the car is warm or cold. Anyone else experience this?
By the way, this has not set a CEL.

My apologies if this has been asked a zillion times, I did search for an answer first.

Thanks in advance!

How many miles on car? and has the MAS/MAF sensor in the intake ever been changed?

As the sensor goes bad it my not set the CEL or codes for a few weeks.

The kickdown position of the throttle is when the bad MAS first exhibits itself.

The car has 97K miles on it, and to my knowledge the MAF/AMM/whatever it's called on these has never been changed.

Never happened to me. Although I never floor the accellerator. Ethan might be on to something with the MAF theory. I never heard that about the kickdown position. If so it fits your symptoms. In the old days if you had hesitation at high throttle position that could mean a clogged fuel filter. Does it run fine at heavy load (going fast up a hill on the highway)? If so then that throws the fuel filter idea out the window. I wonder if I would even notice this since I never floor mine as far as I know. Are you talking all the way to the floor? These are "electronic throttle" so there is no kickdown cable etc. Don't know if that makes any difference. There does not seem to be a set life for the MAF sensors. They can last 50K or they can last 150K from what I have seen on this site, maybe more. There is a theory that changing the air filter more often prolongs the MAF life. I don't know a way to test the MAF other than by swapping it out for a known good one. Hopefully you will get a better answer from someone else. Good luck.

Mike

Air filtration plays a key role in MAF sensor life. The sensor film is easily damaged when bombarded by dust/dirt particles. Not only should the filter be replaced when dirty, the induction system should be TIGHT. No unfiltered air should be permitted to pass through the MAF sensor.

As far as testing goes, if you have the necessary equipment such as SDS, you can read the actual amount of air the engine is using. I used to connect an SDS and drive the car from a standing start, wide open, until it shifted into second gear. At the highest RPM I would note the air quantity (eg. 250kg/h). With a new sensor, the reading would usually be much higher (500+kg/h). Since the faulty sensor is reporting a much lower air quantity the injection duration is adjusted accordingly, reducing the amount of fuel. This results in the lack of power. Nowadays we just read out the fuel trim data. If it's near the limit we replace the MAF sensor and drive the car around the block once or twice. We then re-check the fuel trim data. If it's heading back towards the baseline, it's fixed.

Lastly, Ethan is correct. The CEL only comes on when engine management has adjusted the fuel mixture to the limit.

Ah yes, the fuel trim. I have no way to read it so I forgot about that. So I suppose the fastest test is to read the fuel trim and if it is near limit then the MAF is probably ready to go. You sound like a professional and I obviously am not!

Mike

Sorry to bring this back from the dead, but I just wanted to post an update. I replaced the AMM, and all is well. The car runs perfect again. Thanks to everyone for your help!