During my last road trip I encountered the weirdest issue with my 2011 Hyundai Accent. On the highway the RPMs went down to 0 but I was able to drive completely normal. After I turned the car off, I wasn't able to start it back up again. Only after about 45 min of cooldown, the car started and everything went back to normal. After about 30 min driving I noticed a little stutter but everything seemed normal. But the moment I started braking enough (potentially downshift) the RPMs went back to 0 and the same issue repeated itself.
I brought the car to a nearby mechanic and they couldn't find any error codes. They didn't really try much else since it was Saturday and they were about to close.
I'm thinking maybe a faulty sensor. Maybe related to some heat expansion. The only weird thing is that I'm able to drive for ages with the revs normal as long as I'm not breaking. I managed more than 30 min on the highway on my drive back home. But the second I break a little the whole story happens again.
Any ideas are highly welcome!