Tonyr313

Can anyone help diagnose a problem I have had recently? Facts are below -


-2002 996 6 speed with 68k miles
-occasional rough idle when starting the car cold
-got "check engine, drive to workshop light" - I took it to my Indy and the codes included misfire cyl 4, 5, 6 and running lean
-Spark plugs/coil pack are approx 4 years, 14k miles old
-AOS is original, water pump has been replaced. The oil cap is not hard to remove when I untwist it.
-One month ago I had a new oil filler tube installed as my old one had a very small crack in it. The original oil cap was kept and is on the oil tube (I ensured it was tight and ensured the gas cap was tight)
-I added Techron fuel system cleaner last night and drove about 15 miles. I will continue to put miles on it in case I had a tank of poor gasoline.


Are the spark plugs/coils potentially the culprit despite being a few years old with less than 20k miles? Car is garaged but in heat (Atlanta/Tampa) always and not driven every day.


Indy cleared the codes and said to monitor it. The codes/CEL have yet to appear. Car still not idling properly, sometimes slow to start, and at times the pickup does not seem 100%. Blipping the gas pedal in neutral results in less than typical exhaust note.


Thank you

Hurdigurdiman

You say that the oil filler tube was replaced. To do that job the alternator has to be removed in order to get to one of the bottom bolts holding the filler. Above and behind the alternator are evap lines which over time become brittle. My guess is whoever removed the alternator inadvertently broke or pulled and disengaged one or more of the evap lines causing the CEL to appear. This would also cause the engine to run lean as the system is now sucking in extra air which the computer is unaware of. The computer is only aware of air entering via the Mass Air flow sensor but nothing beyond that point. Thats my guess. I suggest you go in and removed the alternator and check those evap lines. At least that's what happened to mine when I let a 'so called mechanic' work on my car. I had to repair the lines myself.

Barn996

Do you know the specific codes? I would look at coil packs as the reason for your misfire.

Tonyr313

Thanks - I do not know the specific codes. Will continue to monitor. Do the coils really go bad in so little time/so few miles?

extanker

if it was idling rough and all the mechanic did was clear codes you need to find a shop that knows how to use a scan tool.......sometimes just looking at injector on time tells the wrench you have a vacuum leak .there is a long diagnostic tree to follow in some cases for codes .....i guess this shop was busy or you will have to make an appointment and drop it off [costly] .i do not recommend you taking the car apart poking n hoping

Tonyr313

Yes, the shop was busy - mentioned there could be a vacuum leak, could be bad gas, few other things...suggested I drive it enough to get rid of the tank of gas and see if problem persists. Said to bring it back for full diagnosis if continues. I am confident in their ability, it's a Porsche only shop...

TonyTwoBags

My observations with a vacuum leak are higher idle, less stable idle & a bit of sound coming from the line in question.

Coil packs seem like a clear possibility. I'd go easy on driving the car until you get the fuel mixture right & idle corrected. It sounds like there are two issues in my view, but I'm biased by my specific yet narrow personal experience.

Try troubleshooting these:
- cause of idle disruption (vacuum line possible, idle control valve (?))
- cause of misfires (crank position sensor, coil packs main culprits)

Porschetech3

Comprehensive testing of fuel trims, injector pulse widths, fuel pressure, MAF values, will determine if there is an air/fuel ratio problem, and if it's lean/rich. The results/values will determine what tests/checks are done next. Vacuum leaks are the most common culprits.