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Discussion Starter #1
Hi everyone. I have had my '10 M3 since mid June and have had the check engine light come on 3 times due to carbon buildup on the spark plugs. Each of the previous times the dealer cleaned the plugs and turned off the light. This time I am going to have them look at it more throughly. Any ideas on an underlying reason this keeps happening?
 

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Discussion Starter #3
nope, regular unleaded gas.
 

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How's your gas mileage been? Carbon deposits are generally due to an excess of fuel in the oxygen/fuel mixture. Could be a bad O2 sensor, bad fuel injector, or an issue with the computer that regulates the mix.

The dealership should be able to hook up your car to their diagnostic equipment and see what's out of whack.
 

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Discussion Starter #5
Been getting very steady 29MPG since I have had the car.

The first time I took the car in the dealer cleaned the plugs and said it was due to starting and very briefly running the car and then turning it off (said this might have been done at the dealer before I got the car).

The next time it was 3000 miles later and they just cleared the light and held the car at 4,000RPM for a few minutes to burn off the carbon as they just squeaked me in between other appointments becauase they wanted to look at it quick to make sure it wasn't a bigger problem and I could still drive it.

I put the K&N air filter in from my '06 M3 about 2,000 miles ago, so I got the light twice before that was in. Never had this problem on my '06.
 

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Could it be a EGR valve problem? Seems like if the EGR valve was stuck open, it would increase exhaust gases being recirculated, leading to more carbon deposits. That's the only thing I can thing of.
 

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Discussion Starter #7
Thanks for the thoughts, will remember to have them check that. I have an appointment Friday afternoon to have the car looked at. Any harm in driving it until then or should I try to borrow another car?
 

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Could it be a EGR valve problem? Seems like if the EGR valve was stuck open, it would increase exhaust gases being recirculated, leading to more carbon deposits. That's the only thing I can thing of.
Good call! :thumbup: I had this problem on my '02 Protege5 so it seems like a possible scenario.
 

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Discussion Starter #9
Any harm in driving it until I get the car in for service this Friday or should I try to borrow another car?
 

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I think it should be fine for a couple of days, but I don't know for sure. Most likely, your car just won't run very well (rough idle, less power, etc).
 

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Any harm in driving it until I get the car in for service this Friday or should I try to borrow another car?
My old car, 2002 Pontiac Grand Prix, had a thing where if the check engine light came on, the car would go into "safety mode" it would drastically cut performance as well as mpg just to make sure whatever the problem was wouldn't make the engine go KABOOM!

Anyone know if Mazda has this "feature"?
 

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Don't know for sure. When My P5 had a bad EGR valve it performed just as Drrick described, rough idle, low power, sluggish acceleration. Definitely get the vehicle checked ASAP as the carbon buildup will get pretty bad and can screw up emission of left for too long.
 

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Discussion Starter #13
Ok thanks, oddly enough I don't really even notice much of a difference in power. Car still takes off like always.
 

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Is the EGR the same as a PCV?

If it is, in addition to plug problems you also get pressure built up in the crank case which can cause gaskets to leak in the long run.

Also, if this is the same device, check the air cleaner to see if there is any blow back on the underside of the filter.
 

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Discussion Starter #16
did a quick search on the two and they don't seem to be the same. something to bring up though when I take the car in. It does seem to idle a hare rough right after starting.
 

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Yeah, thats what I was thinking...but I'm still not positive..
I think the reason for being unsure is the fact that the car isn't even a year old yet O_O. It should be an easy check the a tech at the mazda dealer....
 
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