Q: Start issues

Recently my van started to have some issues, I replaced the battery and then throttle position sensor on a saturday afternoon, and the next morning i was having some issues starting the van, i started the van and the motor was not responding, then I went back to the off position and the van start normally, so that's the way I’m starting the van for now, trying the first time the start position, if nothing happens, then I go back to off position and the van starts, but recently my van is starting to hesitate to start even when to motor is in a hot temperature....The problem is less than a week old

My car has 125000 miles.
My car has an automatic transmission.