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

You might check the coil packs and wires. Long shot , doesn't quite fit the symptoms but coils can do funny things.

Regards, PK

Coil packs and make sure when you replace them that they are definately plugged all the way in.

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

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.

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.

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.

thanks for the replies..appreciate it

have booked it in tomorrow at the local Porsche dealer..will let you know what they find

Jaay was right..loose coil pack on number 5