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Discussion Starter #1
I just came back from a long trip and my C240 started acting up. The check engine light came on and when the car is stopped there is some slight shaking. It accelerates really slow, not like before... I was thinking it might be the spark plugs or the wires maybe?? If anyone has any ideas, please help!! My nearest dealer is about 200 miles away, so I kinda need to see if it is something simple or if I should take it to the dealer.
Has anyone here had the same problem??

Thanks in advance!
ps.
I have a confession: Prior to the trip I didn't put the premium fuel in my benz! Could this be the problem??
 

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Discussion Starter #2
I put some techron in the fuel system and filled it up with premium.
How long does it take for techron to take effect? Is it instant or does it take one tank?
 

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It's probably not going to be something your going to fix by changing fuel. Most likely the fact that you didn't use premium fuel should have nothing to do with your problem. Especially for a C240.

If your using the correct spark plugs, they should last a good 100k miles before they need to be replaced. So if they're about that old, it could be a good starting point. The spark plug, do outlast the spark plug wires. But plug wires are damned expensive, especially for the whole set. But I do see plug wires start going bad at about 70-80k miles. Things like a vacuum leak or a bad mass air flow sensor can also cause a rough idle or lack of power. If you know of any reputable independant shops near by that are familiar with later model MB's, that might also be a good option.
 

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after doing some research and after OBDII, I made a list of possible causes for this:

Spark plugs- this could be the problem, but I don't know why OBDII showed missfire on 4 cylinders..
wires- could be, but I doubt it..
coil - this might be the problem because 4 cylinders are missfiring

the ultimate problem, I think is the fuel I put in!! If this idling/shaking/low acceleration is caused by the 87 octane I put in, then it could be the sparks or maybe even the fuel pump!!

Any ideas?
 

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I just want to make sure, you have misfires on four different cylinders, right, not a misfire on cylinder 4. Does your scan tool just pull codes, or can you look at sensor values with it as well? I still doubt it's the fact that the fuel in it is 87 octane. But It's possible that maybe it's a bad batch of fuel. That's not uncommon. What codes did you get exactly?
 

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Discussion Starter #6
Yes, four different cylinders are misfiring!! I unplugged the MAF to see if that could be the problem, but no luck.
I bought some spark plugs but did not get a chance to change them.
I don't know what else could be the problem... The car is barely drivable, so I will need to figure it out quick.

ps.
I am not sure what codes it gave me exactly, but it said missfiring on cylinders: 1, 2, 5, 6.
 
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