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Discussion Starter · #1 ·
ok so here it the situation trying to fix a friends car.
She called me and said it was running really rough and she couldnt drive it.
I pulled the codes and it had nothing but misfire codes so I replaced the plugs and all the wires. used factory plugs and bosch wires just like the factory ones. I though I had it fixed fired it up and it idles perfect.
Now here is where I want to pull my hair out.

The car wont accerlerate if pressing the gas pedal more then half way. If it is pressed very lightly it will rev up just fine it hits the rev limiter and everything seems normal but if you floor it it bogs and misfires? The same happens if you drive it. It also seem to be worse when you first start it cold. After it warms up it responds better to the throttle but never acts completely right.
It seems to like to throw a cyl. 4 miss fire code the most and I swapped one of my coils to cyl. 4 and no diff.
I have swapped the mass, and cranksensor from my car (same parts) checked the fuel pressure 45psi it never drops when you rev it or while it is misfiring. it has a fairly new fuel filter. I took a fuel sample and didnt see water. checked for vaccum leaks. What am I forgetting? at a loss! any help or ideas would be awesome! thanks...
 

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2002 ML55 AMG, 2005 Chrysler Crossfire Coupe Limited, 1999 C280
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ok so here it the situation trying to fix a friends car.
She called me and said it was running really rough and she couldnt drive it.
I pulled the codes and it had nothing but misfire codes so I replaced the plugs and all the wires. used factory plugs and bosch wires just like the factory ones. I though I had it fixed fired it up and it idles perfect.
Now here is where I want to pull my hair out.

The car wont accerlerate if pressing the gas pedal more then half way. If it is pressed very lightly it will rev up just fine it hits the rev limiter and everything seems normal but if you floor it it bogs and misfires? The same happens if you drive it. It also seem to be worse when you first start it cold. After it warms up it responds better to the throttle but never acts completely right.
It seems to like to throw a cyl. 4 miss fire code the most and I swapped one of my coils to cyl. 4 and no diff.
I have swapped the mass, and cranksensor from my car (same parts) checked the fuel pressure 45psi it never drops when you rev it or while it is misfiring. it has a fairly new fuel filter. I took a fuel sample and didnt see water. checked for vaccum leaks. What am I forgetting? at a loss! any help or ideas would be awesome! thanks...
Sorry to hear about your friend's problem.

I have to ask:

How old is the MAF sensor from YOUR car which you swapped and WHERE was it bought (i.e. is it a GENUINE BOSCH MAF?)

What I am alluding to is it is quite possible that your MAF sensor too is faulty and functioning marginally thereby defeating your ingenious way of testing whether your friend's MAF sensor is at fault.

When I first read your post I was inclined to say that the MAF sensor on your friend's car is at fault - I have a sneaky feeling that is still the case.

But I'm no expert.:)
 

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Discussion Starter · #4 ·
ok so I swapped in a mass insert that runs good but throws a po140-143 code. The car still acts the same. I though about the o2 as well but wouldnt it throw a code for the sensor or something? all I get is a misfire code and that is only if you try to give it more then part throttle. it will sit and
Idle just as smooth as when it was new. something else I checked was that when depressing the throttle peddle the throttle flap on the motor does open completely even while it misfires.
 

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1998 c230 170K
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I would try a throttle body cleaning with a new air filter for starts. From what you posted so far its pointing to one or both 02 sensors. Sounds like you may have ruled out the MAF, usual cause. Post the mileage and what other thing have been done to the car so people can help you out better. B

http://www.buellwinkle.com/MBOBD2.html
 

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sounds like the throttle actuator could be the culprit.
you need to have it hooked up to the Star Diagnostic(SDS) and look at the sensor values for both the throttle actuator and the acceleratop pedal, for both partial load and full load tests. if the voltages are out of specs, the sensors will be highlighted in black and you will know which one is the cause.
 

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I haven't looked into it on w202 but had same problem with my Jaguar. MAF sensor acts as a supplement to engine management and reacts slowly to changes in air input thus altering fuel. To make the response quicker throttle position potentiometer helps when pedal is pushed down fast and lets maf catch up. If the the throttle sensor is bad, it will lead to the problems described.
 

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s430 2000
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ok so I swapped in a mass insert that runs good but throws a po140-143 code. The car still acts the same. I though about the o2 as well but wouldnt it throw a code for the sensor or something? all I get is a misfire code and that is only if you try to give it more then part throttle. it will sit and
Idle just as smooth as when it was new. something else I checked was that when depressing the throttle peddle the throttle flap on the motor does open completely even while it misfires.
Did you ever figure out what was causing the problem? I am having a similar problem with an S430, it's like the car would choke if i accelerate normally. I have to tap my pedal for the car to even move normally, or not it will sound like it doesn't want to go to the next gear, like if it's stuck on 2nd gear.
 
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