I have a 2008 S40 2.4i that I bought new and do mostly city driving (it has 12,500 miles on it). I treat it respectfully and go by the manual on maintenance. A few months ago the engine surged randomly for a few seconds. The car sputters, is very jerky, the tachometer goes nuts, and it feels like the car is going to die. The only way it has corrected itself is when I stop, then take off again.

Now it's been happening more frequently. It's happened four times within the past month. I took it to the dealer and they found nothing wrong and said the software just indicated a previous "vehicle malfunction," but gave no further detail. Mechanically, everything looked to be fine. As I was driving from the dealership to my office, the same issue happened, so the dealer said to bring it back and they would look into the issue further. A few days later, even before I could take it back to the dealer, the same issue happened twice within half an hour. The car died at a traffic light this time. When I tried to start it up, nothing happened. I waited a few seconds and was able to start it up again.

Took it back to the dealer the next day and they are BAFFLED as to what the issue might be, even after a thorough inspection and test drive. The software indicated no issues or malfunctions this time. If it was the fuel injector, it would have indicated a problem. They said next time it happens to try either of these things: turn off A/C and wait five seconds OR put the car in neutral.

The car feels fine now, but I'm still scared this might be a safety issue. I'm also very disappointed that the dealer says they are SO surprised by this issue and have never encountered anything like it, especially in a car so young.

Thoughts on next steps or what the problem might be?