(Tracking this thread) - I encountered similar problem this past weekend at VIR. Warm up lap of the last session on Sunday, coming up the esses, my car just started running like shit, eventually cutting itself off at South Bend. I was able to coast down the hill, and park it next to the Oak Tree flag station.
When I got towed back into the paddock, I started it long enough to get it onto the trailer. Sounded like shit, RPMs jumping all over the place, and eventually cutting off. Riley took a listen to it for about 15 seconds, and thinks it's a vacuum leak.
Monday morning, I pulled the air box off and noticed that the pop-off valve had cracked off at one end of the spring hinge (non-fixable). Will be ordering a new one.
Fairfax Jim came over and we tested spark and fuel pump, which turned out fine. Started it back up again, and after about 10 seconds of smoke, it started running fine again. Took it around the block, and all seemed well.
I'm still not sure what went wrong (besides pop-off valve), and am not totally sure it fixed itself.
I've got 3 more events until the end of the season, and I'm hoping that it'll survive.