Limp mode?

Our car has been having trouble starting only after pumping gas. It runs fine after about a minute. We have not taken it in because it usually is not bad and will adjust itself.
It has gotten worse, now the last time we filled up it was slow to start and when we started to move forward the power brakes and steering went out along with no longer being in drive even though we did not switch gears.
We tried starting it up again with the same results but for reverse. The car turns on, engine starts, put it in gear, works for about a second and then steering breaks go out, and car switches to neutral.
After about fifteen minutes we tried again and it started no problem, and we were able to drive like nothing was wrong.
We want to get it looked at but have no idea where to begin, we ran a diagnostic on the car and it did not show much.
Any idea what could be going on?