Porsche 991 Power Loss & Jerking: Owners Share Stories

Had the same issue with my 2015 Porsche Cayman S last summer. The symptoms matched exactly what you're describing, power loss, rough idle, jerking during acceleration, and that dreaded check engine light. Took it to my Porsche dealer and they diagnosed a faulty vent line from the tank to the DMTL valve. The line was cracked and causing vapor leaks, which messed with the fuel system pressure. Not a super serious issue if fixed promptly, but definitely not something you want to ignore as it can affect fuel system components long-term. In my case, they replaced the vent lines and did a full system check. The car's been running perfectly since then. I'd strongly recommend going to a certified Porsche dealer for this one, they have the right diagnostic tools and experience with these specific issues.

Thanks for sharing your experience! Glad to hear it was just the vent line issue. My symptoms sound identical to what you had. I was actually thinking about booking an appointment with my local Porsche dealer tomorrow. Do you remember roughly how much they charged you for the fix? Also, any other issues pop up since then? Just wanna make sure I'm prepared for what's coming.

Hey there! Happy to give you an update. Yes, I got it fixed at the Porsche dealer and it cost me exactly 205€ to replace those defective vent lines from the tank to the valve. Since getting that sorted out, the tank ventilation system and DMTL valve have been working perfectly, no more error codes or issues at all! I've put on quite a few miles since then and the car's been running like a dream. No power loss, no jerking, and that annoying rough idle is completely gone. Honestly, it was worth every penny to get it properly fixed at the dealer. They really knew what they were doing with these Porsches. Haven't had a single related issue pop up since the repair, so I'd say you're making the right call going to the dealer. Better to get it done right the first time than mess around with shops that might not be as familiar with these specific problems. Let me know how it goes!

Just wanted to update everyone, got my car back from the Porsche dealer today and wow, what a difference! You were spot on about the vent line issue. They found a crack in mine too, just like yours. Bill came to around 220€, which wasn't as bad as I was expecting. The whole experience was actually pretty smooth. Dropped it off yesterday morning, they diagnosed it right away, and had it fixed by this afternoon. Car's running like new now, no more power loss, jerking, or rough idling. Check engine light's gone too. Such a relief! Thanks again for your recommendation about going to the dealer. They really knew their stuff and I probably saved myself a bigger headache down the road by getting it fixed properly. Feels good to have my Porsche back to its normal self! Gonna take it for a proper drive this weekend to make sure everything's perfect, but so far, I'm super happy with how things turned out. Thanks everyone for the help!