Hertz - Serious mechanical problems twice recently

After renting from Hertz for years without problems, I have had two nearly identical mechanical problems with cars that were potentially serious. In both cases, when I would pull up to a stop sign or red light and take my foot off the accelerator, the engine would start to race. The only way I could control the car would be to shift into neutral. The engine would then slow down and I could continue.

In both cases it could have led to a serious accident and I had to take a lot of time getting back to a Hertz rental office and exchanging the car.

It's probably a coincidence, but it's a little unnerving.