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It seems like I've read somewhere that an iffy crankshaft position sensor can create problems at idle. Any engine monkeys know more about that?
 

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Normal idle speed is not "causing" your random misfire.

It may be causing the real problem (whatever it is) to reveal itself ... but the engine's normal programmed idling speed is not the "cause" - otherwise they would ALL have the same random misfire. Something else is the "cause".

If the misfiring condition is repeatable, take the car to someone who can do a good diagnostic on it.
 

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The "defrost" function turns on the a.c. compressor and does kick up the idle speed to handle the extra load of the compressor at idle, FYI.
When mine is running perfectly, it is very, very smooth.
I wonder if a good tech. with the knowledge of how to index the spark plugs, might be able to improve the random miss?
Injector cleaner might possibly help. I've had a good experience with "Star-Tron", available in the marine department of Wal-mart, simply added to the gas tank.

When firing properly, this engine runs like a sewing machine. Very well, balanced. :D
Any good mechanic should be able to address this. It does not have to go all the way back to Jackson, MS. to be repaired.
MSMURPHREE, where in N. Mississippi, are you? A new MB dealership is opening in Collierville, TN. in the not too distant future. It is owned by Higginbotham Motors, owner of the smart Center in Jackson, and they will be servicing smarts, so they told me. I'm guessing they will be sub-ing the work out from the smart center, to the Collierville Dealership. I work in Collierville, maybe our paths will cross some day? :)
My black Brabus BB Benz, lives five days a week, afternoon, in the Collierville Home Depot parking lot. I'm usually located in the appliance department. Stop by some time.
 

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Idle speed is not adjustable. A misfire can cause a rough idle. A low idle does not cause a misfire. If the car has a misfire then testing is required to determine the cause. You can snag guesses and throw parts all day long but one test is worth about 10,000 opinions and more than one test may be required.

The hard part is finding somebody that can properly test it rather than read a code and toss a part. That applies to any vehicle, not just a smart.
 

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Two words - Air Leak - somewhere between the intake valves and the mass sensor. Air leak would also include any kind of hose system that uses engine vacuum to do anything. At any speed above dead idle, the % of total air going in to fuel going in through the throttle body and measured is near perfect as the leakage air is an insignificant percent. At dead idle, with most of the air now unmeasured by the fuel injection system, the leakage air % increases until it runs LEAN enough to misfire. The lower the rpms go, the worse the condition. Fuel injection decreases and it just runs leaner and leaner. The worse the air leak gets, it'll reach a point where it won't even idle at all.....

Pray it's not an exhaust valve leaking, sticky exhaust valve, leaky head gasket, warped head, or anything like that as THIS car's overhauls are more expensive than a Boeing 787 overhauling both jets!
 

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Two words - Air Leak - somewhere between the intake valves and the mass sensor. Air leak would also include any kind of hose system that uses engine vacuum to do anything. At any speed above dead idle, the % of total air going in to fuel going in through the throttle body and measured is near perfect as the leakage air is an insignificant percent. At dead idle, with most of the air now unmeasured by the fuel injection system, the leakage air % increases until it runs LEAN enough to misfire. The lower the rpms go, the worse the condition. Fuel injection decreases and it just runs leaner and leaner. The worse the air leak gets, it'll reach a point where it won't even idle at all.....

Pray it's not an exhaust valve leaking, sticky exhaust valve, leaky head gasket, warped head, or anything like that as THIS car's overhauls are more expensive than a Boeing 787 overhauling both jets!
Larry, you really should get your facts straight before spouting this nonsense. The smart has no mass air flow sensor. It is a speed-density system and as such a vacuum leak will not cause a lean condition but it will increase the idle speed, not decrease it.
 

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Oh lord another additive. I just watched the Star Tron vid on their website.
If we used all the incredible fuel additives offered, we'd have no room for actual fuel.
Having said that, I've never personally tried Star Tron. It may indeed be magic.
 
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