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Car misses at Idle in drive, but drives fine?

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Old 02-11-2011, 01:06 PM   #1
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Default Car misses at Idle in drive, but drives fine?

Ive noticed this sitting at a light. If Its in drive (A4 98 Z28), I can feel the car miss on 1 cylider. The engine will make a full firing order rotation and miss, then rotate again and when it hits whatever cylider its trying to fire on, it misses again.. I cant pinpoint where its misfiring. No check engine lights for misfire, just for Oxygen sensor.

But it drives fine. Could it be something else besides Plugs?
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Old 02-11-2011, 01:43 PM   #2
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Failing 02 sensors can cause misfires. If you have a code for it go get a scan to see how they are switching with the engine running at operating temp.

As far as the misfire...it can be a dozen things. Quick checks.....make sure none of the spark plug wires are touching any parts of the metal exhaust manifold piping. make sure they are all snapped on. If you know which cylinder is missing, swap wires with another cylinder to see if follows that wire. Then after that, you can do the same with that coil. Spark plug in that cylinder might be cracked. Might have a dirty fuel injector in that cylinder too. Or bad injector. Or bad wiring to that injector.

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Old 02-11-2011, 01:50 PM   #3
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Hmm.

But its just weird how it ONLY does it at idle. Driving it runs fine
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Old 02-11-2011, 02:02 PM   #4
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Sometimes a dirty fuel injector can be slightly dirty.....at idle the fuel has trouble atomizing. But under throttle the fuel pressure rises and can easily overcome that dirt. Until it gets really dirty.

Electrical problems do that also........something small causing an arc is more apparent at idle.....but again, under thottle, electrical output rises in the system and can overcome that small problem.

Its highly likely that one of the things I mentioned is your issue, but there's still other things that can cause misfires.

Try to find out which cylinder it is through a scan. Maybe even go get scanned for free at an auto parts store. It might show something.

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Old 02-11-2011, 02:03 PM   #5
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Same with a dirty fuel filter......at idle it will stumble and miss. But under throttle that small clog will be overvcome from the rising pressure. Until it gets really clogged then your screwed.

Bad battery can also cause misfires.

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Old 02-11-2011, 02:07 PM   #6
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mine is doing the same thing. i scanned it before and it showed cylinder 8. i replaced spark plugs and wires and i can still feel it but it doesnt show up on the scanner. ill report back if i figure it out.
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Old 02-11-2011, 03:13 PM   #7
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Originally Posted by southpaw0314 View Post
mine is doing the same thing. i scanned it before and it showed cylinder 8. i replaced spark plugs and wires and i can still feel it but it doesnt show up on the scanner. ill report back if i figure it out.
Run a FULL can of SeaFoam through 1/8 - 1/4 tank of gas......that should clean out all the injectors pretty well.

Could be a coil issue too. Might want to swap it with another and scan again to see if that coil follws to the other cylinder.

You can also swap the injectors to see if its dirty or bad.

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