Is occasional misfiring on an idle engine something to be concered about?

I have noticed that my engine has an occasional misfire every 2 or 3 seconds when its sitting idle. I've had plenty of cars in the past which did this and considered it fairly "normal" but I don't know if I should expect it on a brand new car (ok- 12 months old) modern engine such as the F20C.

Its the type of misfire you can detect by listening to the exhaust or just putting your hand on the valve cover while its idling and feel the occasional jump.

-B

 

not sure its a misfire, but do recall reading about this. mine does it too. more like a very brief engine stall (lack of air or fuel). someone once posted that it could be the gasoline (although i always use name brand premiums), or moisture in the gas. as long as it doesnt do it on acceleration you should be o.k.- mine is not every time it idles, but just sometimes for no reason.

 

That would make sense wannabe... Which leads me to another question: Whats the consensus on alcohol additives for removing the water from the gas (gasline freeze additives)? Will this hurt our engines? The guy on MotorWeek said they were safe as long as it was the pure alcohol version. I think they also use these little yellow bottles of alcohol to make home brewed amphetamines(trivia).

I wonder if this idle has anything to do with the MTBE additive they force on us here in Indiana. Its supposed to burn the fuel cleaner, but it actually just seeps into the ground water from the tanks and causes cancer! Hurray! Either way you win! No more smog or you're dead so you wouldn't notice the smog.

I suppose these questions should be posed in the under the hood forum...

-B


[Edited by bguernsey on 03-26-2001 at 12:59 PM]

 

bguernsey, the F20C is really sensitive to additives like MTBE. Check your owners manual. It gives max %'s for various additives. See if your local gas is close to or exceeds those percentages.

 

The information I was able to find suggested that our Reformulated Gas contains Ethanol instead of MTBE. But I'm not sure of that. The big question is- what to do if you live in a state where this is mandatory (like Indiana)

-B

 

MTBE 15% maximum...
Ethanol 10% maximum.....

Methanol (or wood alcohol) 0% or damage may result. If you use alchohol you will need to replace the O2 sensor and catalytic converter to return the system to normal.

 

Wow... I guess I have to check that out!

I was under the impression that misfiring (even at idle) is somewhat harmful for the engine (the catalyst in particular by unburnt fuel in the exhaust system), and will cause the OBD system to give you an error through the check engine light.

The OBD system is designed to detect misfiring, through uneven crancshaft rotation, because the misfiring will most probably result in emissions that are too high and the possibility of catalyst breakdown.

Let us know what your findings are! (Please)