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Old 05-06-2011, 10:40 PM   #1
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Help!!..misfire no CEL

HI.. need some help
have a intermittent misfire below 2000rpm on my 2002 2.7 manual Boxster.

I removed the throttle body 2 weeks ago and cleaned it, since then have a misfire at low revs. No CEL , just rough running.Clears over 2000 rpm, but misfires badly when it drops below this.Does not happen all the time, will run fine for 5 km or so, then misfire.

Any suggestions??

thanks
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Old 05-09-2011, 06:18 AM   #2
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You might check the coil packs and wires. Long shot , doesn't quite fit the symptoms but coils can do funny things.

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Old 05-09-2011, 08:24 AM   #3
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Coil packs and make sure when you replace them that they are definately plugged all the way in.
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Old 05-09-2011, 02:54 PM   #4
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If the missfire happened after you removed the throttle body for cleaning, I would also go over your work and double check all the connections, both electrical and vacuum lines
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Old 05-10-2011, 10:48 AM   #5
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Misfiring is usually related to an issue with the engine timing or fuel/air mix. Usually, you'll get a CEL if the fuel/air mix is off (this is what the O2 sensors monitor), so the first place to look for a misfire with no CEL is the engine timing:

The input comes from the crankshaft position sensor. If this sensor isn't working reliably, the timing will be off.

The output is through the coil packs/wires. If either of these aren't working properly, the timing will be off.
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Old 05-10-2011, 11:08 AM   #6
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what if the lead up to this was a bad maf which lead to a rich af ratio. could it be fouled plugs? i only ask, im not trying to hijack, ive just had similar problems.
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Old 05-10-2011, 12:33 PM   #7
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Because it's cheap and easy I'd first disconnect the battery and then follow the procedure for a throttle "relearn/recalibration". Hook up the battery, turn the key on but don't start the motor, leave key on for 60 seconds, turn off key and remove.

And don't woryy about the CEL - it'll come on eventually, lol. The other poster who suggested a vacuum leak due to a detached vacuum line could be right though.
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Old 05-11-2011, 03:20 AM   #8
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thanks for the replies..appreciate it

have booked it in tomorrow at the local Porsche dealer..will let you know what they find
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Old 05-13-2011, 01:05 AM   #9
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Jaay was right..loose coil pack on number 5
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