What else to replace after MAF? - PeachParts Mercedes-Benz Forum

Jase25 · #1 06-01-2009, 06:04 AM

Hi All,

I bought a 1998 C200 manual about 2 months ago. Soon after I realised it was lacking in power and would intermittently 'back down' when travelling at speed, as if I'd taken my foot off the accelerator.

It was also very very sluggish at low revs, so much so that turning across traffic was a risky afair because you couldn't get speed on pull off.

I did some reading and eventually replaced the MAF sensor. Since then there has been more power but still not what I would expect. At times it is still sluggish at low revs. So it is overall a bit better but not right. It also has a very distinct exhaust smell when cold that smells like it's running rich.

Fuel consumption has also not been great. I've been getting around 8km/ltr (or 18.93mpg if my calculations are correct).

So, what else needs to be replace after running a bad MAF for a while?
What else should I check? How do I get this car to perform at full potential?

Other info:
It has +- 180,000kms (112,500miles)
It has a full service history at the Merc Dealership (big selling point for me but been dissapointed so far...)

Thanks,
Jase

G-Benz · #2 06-01-2009, 10:44 AM

Sounds like the bad MAF caused a rich running condition that may have also fouled the O2 sensor.

Do you have a "check engine" light on?

david s poole · #3 06-01-2009, 06:55 PM

this is the 4 banger right?the next common problem is the throttle body on those cars.it is an electronic accelerator and they wear out around 150k miles.

mpolli · #4 06-02-2009, 12:19 AM

Mine was a bit underpowered after I changed the MAF since I didn't reset the adaptations (I never could figure out how other than go to the dealer). So it took a while for them to "re-adapt". You might scan for codes and see if any are there.

Jase25 · #5 06-02-2009, 02:42 AM

Quote:

Originally Posted by mpolli

Mine was a bit underpowered after I changed the MAF since I didn't reset the adaptations (I never could figure out how other than go to the dealer). So it took a while for them to "re-adapt". You might scan for codes and see if any are there.

I did try remove a fuse for 30 seconds to reset it as suggested by someone else on the forum. I can't remember which one it was, I think number 30 something.

Does anyone know the correct way to reset the adaptations? Should I just disconnect the battery for a while? I would think that this would not help. Lots of service work requires the battery to be disconnected and I'm sure MB would have set it that the car would not loose it's "memory" from just disconnecting the battery....

Oh, and the check engine light is not on

Jase

Jase25 · #6 06-03-2009, 02:26 AM

Quote:

Originally Posted by david s poole

this is the 4 banger right?the next common problem is the throttle body on those cars.it is an electronic accelerator and they wear out around 150k miles.

Ok I did some reading up on "resetting the adaptions". My thoughts are I've been driving the car for about 2 months now and I'm sure it would have "adapted" to the new air flow meter. At the time I also tried the "remove the fuse" reset thing.

So, now per the posts it leaves the 02 Sensors and possibly the throttle body...

Is there any way to diagnose these items?

Thanks,
Jase

mpolli · #7 06-03-2009, 12:47 PM

I am no expert but I think there are 3 ways to address O2 sensors:

1) Replace them and cross your fingers

2) Measure their voltage in operation (search for this info)

3) Get an OBDII monitor and monitor the O2 function that way. I have a ScanGuage II and I recommend it to anyone with a post 1996 car. It does just about everything you could imagine and comes in really handy at times like this. As I recall I had to program it to read the O2 sensors since that wasn't preprogrammed, but they explain how to do that. The guy next to me at work got one also and likes it, but we are both electronics guys so maybe that is why.

Keep in mind the O2 sensors may have nothing to do with your problem. The throttle actuator was mentioned previously. I don't know how those fail.

Jase25 · #8 08-14-2009, 04:49 AM

Ok guys I don't know what to do now. I sent my 1998 C200 in to get scanned this morning. There were no codes found! But the car is running really badly! I'm getting just over 7km/litre and there's no power most of the time!!

What do I do now. How would I know if the throttle body is bad?

brookspw · #9 08-14-2009, 09:58 AM

Can someone explain exactly what the MAF sensor does vs what the Throttle actuator do? I'm trying to get a feel for the job of each and, therefore, the symptoms of a problem with each of them vs the other.

Thanks -- I'm pretty much having the same issue, but I have surging idle, too.

mpolli · #10 08-14-2009, 03:11 PM

I can only give you a basic explanation:

The trottle actuator is just the butterfly valve in the throttle. In the old days there was a cable connected from the gas pedal to the valve. The 1998 has an electronic (motor operated) one. I don't know about 1994.

The MAF sensor measures the amount of air going in the engine. It sends this information to the ECU, which then controls the injectors to add the correct amount of fuel.

You didn't ask, but the O2 sensors then look at the exhaust and see if everything was done right, and help the ECU make any corrections needed to make the air/fuel ratio "perfect."

Search on surging idle, which is often caused by leaking or disconnected vacuum lines.