is this maybe the coil packs? it is the 2008 x51, and this just started maybe a week ago, no check engine light and when it is warmed it is fine and still accelerates as far as i can tell, like always... this probably won't show any fault codes with durametric, will it? hmmm, ii can try, though i just got a mac and seems to me i heard that durametric doesn't work on mac, i lookitup...

 

It is not a miss if the CEL is not coming on either steady or flashing and when you read error codes there are no pending misfire error codes.

I can't speak with direct experience with the 997 engines but the engines in the older models, at least in my 996 Turbo, run a bit rough at idle after cold start.

But after I let the engine idle a short while -- the length of time I let it idle depends upon the ambient temperature, colder means more idle time -- the idle smooths right up and idle speed drops to near hot idle speed.

By a bit rough I mean the engine does sound like it is borderline misfiring. I can add that a few times the engine did actually misfire (with the CEL and error codes): One time after being out in the rain all night and another time out overnight when a heavy fog rolled in; the engine was noticeably rougher than usual to the point I noticed the roughness and was just thinking misfire when the CEL came on.

At other times, most of the time save the couple of exceptions I mentioned above -- I can hear -- faint though but real nonetheless -- backfires in the exhaust.

This is a sign the engine is running rich which is done on purpose to feed unburned fuel to the converters which when fed air from the secondary air injection pump will burn and heat up the converters quicker.

Absent a CEL, absent any pending error codes, and with no real drivability problems I do not think there is a real misfire problem with your car's engine. My WAG is it is just the normal cold engine roughness.

Remember these are rather highly tuned engines that have to deliver grocery getter tractability and yet blinding acceleration and high v-max when called upon to satisfy the claims Porsche makes for these cars so if they idle a bit rougher than a Caddy when cold I think that is to be expected.

Also keep in mind that just a moment or two after the cold engine fires up the VarioCam Plus system kicks in and switches the engine to operate in low intake valve lift mode. My Turbo engine exhibits a very brief but noticeable kind of hesitation/almost a cut out (accompanied with a quick dip then recovery of the oil pressure) when this switchover occurs.

You are certainly free to have the car checked out by a qualified tech. Be sure you know how to reproduce the behavior you are worried about then take the car to a shop and duplicate the behavior and get a trusted tech's opinion regarding the behavior.

Even without a CEL or pending codes or other drivability issues he may hear/see something that warrants further investigation.

 

How many miles? Maybe fouled plug(s), dirty MAF, dirty Throttle Body?

 

has 27000 km's, the MAF and throttle body, could be...just didi the plugs about 5k km's ago, i was thinking the coil packs, i always assume the worst...or expensiver things, not that there are any inexpensive pieces in there...and thanks for the informative reply macster, i lean something every time i read one of your posts, some would say i don't drive her hard enough, but i don't buy that, i don't baby the car but i don't hang out by the red line either...

 

you just reminded me of another thing that happens with the car that maybe the variocam is causing...sometimes when i come up to a light, say, and go from 2500/3000 revs to idle at the light it goes to idle and seems to dip below and then pops back up to normal idle, very short sequence and not every time, though i don't pay that close attention to it cause it doesn't put me in mind of impending doom...anyway, i just thought it could be variocam adjusting itself...possible?

 

This may be a totally erroneous answer, but our cars have a rather heavy flywheel to rotate. Maybe as the revs fall this spinning mass drags the RPMs down below what the computer likes to see, so it steps in and adds whatever to bring the idle up to spec. Do you happen to have the A/C on at the time? That's another drag on the system.

 

Try different gas.
Had my engine feeling like misfire when cold. Moved from perto-canada 94 to esso (Exxon) 91 and problem resolved.

 

My 2010 997.2 Carrera S does exactly the same admittedly only for around 10 seconds or so and only when cold and no CEL. More of a brief hesitation than a miss. Dealer claimed "they all do that sir". Does not particularly bother me and having recently replaced the plugs and checked that all coil packs are OK, no improvement. Will try cleaning the MAF and throttle bodies but not confident that this will make any difference. Beyond that, think we just need to ignore and enjoy the car when it warms up !