WinterPorsche

Hi all,

Picked up a 2013 Cayman S PDK a couple of months ago. I noticed pretty early on that the car, when stationary, has a hunting idle, usually in the 600-800rpm range, although sometimes it has dropped to 400rpm and the car has felt like its about to stall, and I've seen it go as high as ~1100rpm. The car has been driving fine so far, and there's no warning lights on the dash.
I took it in for a service about a month ago and asked the specialist to look at it, they were pretty stumped though as they said no codes were coming up and despite the throttle body being filthy, a clean didn't seem to fix the problem. They suggested it might be the air oil separator as there was some mist around the part, but if I'm honest they didn't sound totally convinced and could've just been trying to come up with some form of solution. When I phoned round for quotes at other garages, they all actually tried to talk me out of it as they said AOS failure is practically unheard of with the 981s, so I've decided against getting it replaced until I'm sure its that.

For peace of mind, I bought an OBD scanner off ebay and checked for codes myself, but none came up for me either.

Does anyone have any thoughts? The car may be driving fine at the moment but its a noticeable issue and I'm worried it may be a nasty underlying problem which'll become apparent somewhere down the line, and I don't want to chuck money at it unless I know it'll 100% fix things.


Edit: Spark plugs were changed at the service.

afflux

My car behaved the same way on idle after a cold start. I recently changed my spark plugs and coils and noticed the idle is much smoother now.
Could potentially fix your problem, and worth doing since you probably don't know the last time they were changed.

WinterPorsche

Sorry I should've added at the service the spark plugs were replaced.

colnagoG60

Does the car sit often? I had this problem with my '13 Jetta GLI. Prior to COVID, I spent a tidy sum on some really bad hesitation, which included a walnut blast, new plugs, etc, etc, and turned out to be what I originally told the mechanic to check, a faulty O2 sensor. That said, car sat for long periods of time after COVID hit, and when I started driving it again, I was getting the bouncing tach during startup/idle. I've since been driving the car more, and problem went away. If the car was a garage queen, you may just need to drive it so ECU can re-calibrate. I failed/had to retest an emissions test because of the same. Emissions test tech told me that the car had to be driven certain mileage, within a certain number of hours or test will auto fail.

WinterPorsche

Thanks for the suggestion but unfortunately no, I drive it at least once a week.. Looking at mileage reports it doesn't seem to have sat for a long period of time earlier in its life either.

subshooter

It may be the coil packs (ignition coils). They cost a few hundred bucks and essentially no labor when replacing the plugs. Unfortunately, you just did that. I believe misfires due to the coil packs would give you a code though.

gedwin

Also,
Regarding the A/O separator, a bit of mist around the unit would be normal. The original part has a small vent to atmosphere that allows a tiny bit to exhaust. The new updated part has this vent closed off. I discovered this after replacing mine when I walnut blasted my valves.

tomekz

Any chance it could be injector related?

Kitc2246

How many miles? The DFI engines are susceptible to build up on the intake valve since the fuel is injected after. If really bad a walnut blast is the solution. Is the cold idle stable? Is it smooth on acceleration and at speed? A coil pack misfire should give a code, but have heard other with symptoms and no codes. As suggested I'd run some injector cleaner to see if that helps. 981 uses a manifold absolute pressure sensor instead of Mass Air Flow, but seems the computer is hunting for the right gas/air mixture at idle. When were the two engine air filters last changed?

thecajunboy

I'd try a good injector cleaner and a tank's worth of Italian tune ups.

okie981

Possible vacuum leak in intake manifold or dirty throttle plate. Go to LN Engineering YouTube channel and watch Tony Callas videos. There's one on vacuum leaks and throttle plate cleaning.