Stuttering under hard acceleration.

[ZX10R]

Hi All,

I have a 1995 C200 Auto with 45,800 miles on the clock.
It has developed a slightly annoying problem over the last few weeks:

The car will accelerate perfectly whilst cold. I can push the pedal all the way down and it will accelerate smoothly.

Once it warms up, if I do the same thing it splutters and backfires up to about 2,000/2,500RPM then picks up and accelerates smoothly to the red line.

If I accelerate gently it will go from a standstill to redline with no problem. If i have the car in park and I put my foot down it also judders and then picks up (so no load on it and it does the same thing.)

I think the idle is very slightly off as well, it seems to hunt maybe 50rpm up and down and every now and again the car will judder slightly.

I had the ECU fail on me and I replaced it about 6 months ago, and at the same time I did the HT leads, coils, spark plugs and got the wiring checked out.

I suspect this may be a MAF issue, but is there any way to check this? I want to take it to a mercedes specialist but if it wont show up on the fault code readout I'd rather not pay for that ;-)

Thanks for any responses!

[Len013091]

I had this problem when my MAF failed, but I have a code reader so my problem was easily solved.

[xvvvz]

Can you go by the parts store and have the codes read by borrowing their free scanner? You can always try the CRC MAF spray cleaner. Sometimes that helps.

[ZX10R]

Originally posted by Len013091
I had this problem when my MAF failed, but I have a code reader so my problem was easily solved.


Did your check engine light come on? I have no errors showing on the dash at all...

I guess i'll bite the bullet and get the guys to plug it in and see what it is complaining about today :ermm:

[c280nz]

id try cleaning the maf first!
you can get special cleaner for that job from your local general auto store.
and if this fails then take the next more expensive step of the stealership.
cover the 10$ option first :-)

[ZX10R]

Right, took it to a Merc specialist on Sat who plugged it in and checked out the fault codes.

The real time engine readouts first said it was idling at 3,500RPM with a coolant temp of -42C, then he reset all the fault codes and plugged it in again and it was reading idle speed 2,500RPM and coolant temp 24C. Both were rubbish, since it was idling at 700ish and the coolant was at a steady 70C (ish).

I've booked it in for thursday and they are going to spend a couple of hours looking through it to see exactly what the problem is.

BTW, Where exactly is the MAF sensor on a 95 W202? Here is a pic of the engine bay:

http://www.btinternet.com/~f.beck/IMG00139.jpg

[Espresso]

You have the C200. Is that not a diesel engine? If it is you do not have a MAF.

[ZX10R]

Originally posted by Espresso
You have the C200. Is that not a diesel engine? If it is you do not have a MAF.

Sorry forgot to say I am in the UK - I guess we have different model numbers? The C200 is a 2 litre petrol here.

[Green Lantern]

http://img505.imageshack.us/my.php?image=img00139qa5.jpg
the MAF should usually be located in the red section but by the looks of it, its not there.

[Espresso]

LOL......

Have long have you owned this car?

[xvvvz]

>>the MAF should usually be located in the red section but by the looks of it, its not there. <<

I was wondering if the MAF housing was just rotated so that you could not see the MAF because it was on the other side from the camera position. FWIW, the Russian parts site shows an MAF on both a normally aspirated and kompressor C200.

[ZX10R]

Originally posted by Espresso
LOL......

Have long have you owned this car?

Not sure what is funny? I've owned it for about 8 months.

I thought it was under the red section as well, but there are no wires or anything attached that that part of the air intake.

Just to the left of the throttle body there is some kind of sensor whick clicks into the air intake. It has an almost V shaped thin wire which goes about 1/2 way into the air intake?

http://www.btinternet.com/~f.beck/airintake1.JPG

[OzC36]

What you describe, might be the engine (inlet air) temperature sensor. See photo at this link is.

http://www.autohausaz.com/search/product.aspx?sid=tuxg4cf0mfmchc454x5nvi55&makeid=800016@Mercedes&modelid=1195433@C220&year=1995&cid=temperature@temperature&gid=5080@Engine%20Temperature%20Sensor

Your MAS should look like the one in the photo below and should be situated exactly where Green Lantern showed in the red area:

http://www.autohausaz.com/search/product.aspx?sid=tuxg4cf0mfmchc454x5nvi55&makeid=800016@Mercedes&modelid=1195433@C220&year=1995&cid=22@Fuel%20%26%20Air%20System&gid=5068@Air%20Mass%20Sensor

The mirth exhibited on this thread relates to the fact that no one has ever seen a Merc with a "missing MAS" before. And the fact that your car apparently runs without a MAS is a revelation that we find hard to believe. Hence the comment about how long have you owned the car ...and what the hell else might be missing!

[ZX10R]

Originally posted by OzC36
What you describe, might be the engine (inlet air) temperature sensor. See photo at this link is.

http://www.autohausaz.com/search/product.aspx?sid=tuxg4cf0mfmchc454x5nvi55&makeid=800016@Mercedes&modelid=1195433@C220&year=1995&cid=temperature@temperature&gid=5080@Engine%20Temperature%20Sensor

Your MAS should look like the one in the photo below and should be situated exactly where Green Lantern showed in the red area:

http://www.autohausaz.com/search/product.aspx?sid=tuxg4cf0mfmchc454x5nvi55&makeid=800016@Mercedes&modelid=1195433@C220&year=1995&cid=22@Fuel%20%26%20Air%20System&gid=5068@Air%20Mass%20Sensor

The mirth exhibited on this thread relates to the fact that no one has ever seen a Merc with a "missing MAS" before. And the fact that your car apparently runs without a MAS is a revelation that we find hard to believe. Hence the comment about how long have you owned the car ...and what the hell else might be missing!

LOL Yep... please believe me, I'm not a complete idiot guys :-)

I think it uses a manifold absolute pressure sensor rather than a manifold air flow sensor, silly me!

It has an air tube going from the throttle body to the ECU and I guess that is how the ECU reads the MAP.

Wonder if the ECU might be on its way out again... at least it is still under warranty from the people who repaired it!

[OzC36]

Trust me, no one is laughing at you.

It is just that the Merc engine in question, (and most Merc engines for that matter) are computer controlled. As one of the necessary inputs they need to know mass flow of air through the intake. This is accomplished by a "Mass Airflow Sensor" device which employs a hot film sensor. The amount of cooling of the hot-film sensor is related to the volume, temperature and speed of the airflow in the intake. This is measured, or sensed, and is transmitted as a change in voltage of an electrical signal to the ECU. I assume that the temperature sensor also in the intake just prior to the throttle body is used to help correct for the change in cooling effect to the hot-film sensor purely by temperature so that true air mass can be deduced. The ECU also uses other sensors including the temperature of the coolant, the camshaft sensor crankshaft angle sensor, knock sensors etc, etc.

So, how your engine can be made to work apparently without a MAS to determine the mass flow of air in the intake and sent that signal to the ECU is a puzzle.

I am sure there is a perfectly logical explanation, but it is not obvious to me at this stage with the data you have supplied.

[ZX10R]

Originally posted by OzC36

So, how your engine can be made to work apparently without a MAS to determine the mass flow of air in the intake and sent that signal to the ECU is a puzzle.

I am sure there is a perfectly logical explanation, but it is not obvious to me at this stage with the data you have supplied.

Check up one message - looks like it uses a MAP sensor (which is actually part of the ECU) as opposed to a MAF sensor. :D

[Len013091]

My car will run without a MAF, just not very well. The ECU calculates the fuel based on the engine rpm, IAT, and the MAP from what I've read. Are there any wires that look like they should be connected laying in the engine bay?

[Espresso]

I am not laughing at you. Just the fact that you car is running without one( yes, they can run but not very good).
YES, your car does have a MAP sensor, BUT it should also have the MAS/MAF/AMM..whatever you wish to call it. My car is a '00 & has both. Most Mercedes have both, especially in the mid 90's & up. It's just a small little box with vac hoses connected to it. Mounted on the firewall.
How long has this stumbling on accell been happening? I can tell you, that I can unplug my MAF & have the EXACT symptoms you have(you do this to test it ). My car does not have OBDII so I do not have a MIL or any other light that tells me that something is wrong, so I have to figure out what may be wrong by just disconnecting things, testing with a DVOM...or just plain getting lucky.

[ZX10R]

Originally posted by Espresso
I am not laughing at you. Just the fact that you car is running without one( yes, they can run but not very good).
YES, your car does have a MAP sensor, BUT it should also have the MAS/MAF/AMM..whatever you wish to call it. My car is a '00 & has both. Most Mercedes have both, especially in the mid 90's & up. It's just a small little box with vac hoses connected to it. Mounted on the firewall.
How long has this stumbling on accell been happening? I can tell you, that I can unplug my MAF & have the EXACT symptoms you have(you do this to test it ). My car does not have OBDII so I do not have a MIL or any other light that tells me that something is wrong, so I have to figure out what may be wrong by just disconnecting things, testing with a DVOM...or just plain getting lucky.

BTW Thanks for the replies everyone. :cool:

It has been happening for about 2-3 weeks now. I'll have another good look around and make sure nothing obvious is disconnected. The car has been running perfectly for 6 months before this. :(