WP0

I've owned my 2015 991.1 Carrera for six years. I puchased it when it was two years old, and had 10,000 miles on it. Presently, it's eight years old, with 35,000 miles on it. Ever since I owned it, it has always had somewhat of a rough idle, but I assumed that this was normal for Porsche 911 sports cars. The engine would slightly to moderately vibrate the entire car, but seemed to me like a normal "sports car" idle, and the idle speed would vary a bit, say from 600-800 RPM. Lately, in the past few months, I noticed that the car would idle more roughly when sitting in traffic, and even would rarely slightly rock (this only maybe happened once a month), as if a misfire had occurred, but there have never been any fault codes, nor misfires that would trigger any warning lights on the dash.

Over the past six months, I been pondering whether or not to replace the spark plugs, as the car only has 35,000 miles on it. However, it does meet the time criterion for replacement at eight years old. I had the four year maintenance done to its full extent at the local dealership four years ago, and they replaced the spark plugs then, and nothing changed about the engine's performance at that time.

Since the weather was so nice this weekend in Florida, I decided to do some maintenance on the vehicle while I parked it outside to enjoy the pleasant breeze and perfect weather: I replaced not only the spark plugs (which were four years old), but also the coil packs, which were eight years old, and original parts. The process itself was rather simple, since I've done the basic maintenance for the car over the past four years. There are many threads and a few videos which are helpful. I would add to those threads that multiple extension bars, varying from 2" to 12", and swivel / univesal joints are very helpful, and possibly essential, if you're going to torque everything properly. So, I did that yesterday.

I took the car out for a spin this morning to see if I could notce any changes to the driving, etc. After the engine warmed up, I immediately noticed a couple of things as I came to my first stop: the idle was smooth as ice (reminiscent of a Cadillac idle, which is almost too smooth for a sports car), and the RPM was steady, and held right around 750 RPM. I drove for 45 minutes, and at each stop, the change in temperament of the idling was consistent.

I was also curious about one other thing that I've noticed over the years: would that engine whirr / rattle at 3200-3400 RPM go away. I kept the engine in manual mode for the entire drive so that I could keep the engine between 3000-3500 RPM, and I noticed that the rattle part of the whirr had markedly diminished, and that the whirr sounded smoother than previously, but was still present when I would drop off the throttle from 3300 RPM to idle speed.

Since I had the spark plugs replaced without any change to the character of the engine, I suspect that I could've just changed the coil packs to the same effect. Now, off to change the oil and filters. . .but I think I'll wait until the mileage limit of 60,000 before I get the PDCC reservoir replaced. . .

Levy

i just commented on a thread with a similar topic. my 2013 C2S tach needle doesn't stay planted/rock steady at idle but it doesn't shake or vibrate either. the rpm's vary a bit but not the 200 rpm variance you pointed out. i'd call it 700-800 at worst....maybe more like 750-800. slight movement on the tach needle is all i see. have never "felt" or heard anything that coincided with the slight rpm variation at idle. just a tiny bit of needle movement/fluctuation/float. bought my car almost 3 years ago. it had good service records from the previous single owner, which were all done at the original selling dealer. the only item that wasn't spelled out specifically as being done were the plugs, although they did list the 4 year service as being done. not knowing *for sure* if the plugs and/or coils had been changed made me take advantage of a "while we're in there" plug change discount while having 2 recalls addressed at my local P dealership. car was running fine but i figured why not for a few hundred bucks. one less thing to think about/consider. noticed zero difference after the plug change. remember thinking that i probably just wasted some money on the ride home.

Absolutly believe what you're saying and glad things worked out well for you. just wanted to point out that your symptoms seem to have been much worse then what i (likely others too?) were referring to as the normal movement of the tach needle. especially your noted "significantly more roughly when sitting in traffic, and even slightly rock, as if a misfire had occurred"....which i agree does not seem normal to me either (just like your 200 rpm tach needle movement)

Bud Taylor

The PDCC bottle for some unfathomable reason has an internal filter. I am of the mindset that this filter getting dirty or contaminated (water ??) may be what causes the premature documentated failures of the pdcc at $2500 a side. On my 2012 i changed it twice now at the 6 year intervals and my original pdcc has had no failure. At an indy who allowed me to bring bottle the job was 400 in labor (600 in internet parts) and my understanding is there is a bolt which is near impossible not to bugger which causes other problems (a friend and I did plugs and coils no problem). Ymmv.