Ignition or fuel regulator/pump?

One of you told me your mother in-laws Dodge minivan was doing the same thing a while back. My wagon's ignition when I turned would do nothing unless I let it turn back about halfway then turn it back on and start. Not every time about two times in last 6 months! Alright it's still shutting off sometimes when I slow down to stop or turn into a parking spot and if I hurry and put it in D and start it, it starts but goes to limp mode. Then I shut it off it put it back in Park then wait for 5 seconds. Start it and normally put it in D it drives fine! It's done this 2/3 x past 6/7 months. Could these two things be one or separate no codes well had one a couple weeks ago for p0420 cat slow response but cleared it and hasn't come back? Thinks it's the fuel pressure regulator/pump or the ignition switch. Crank and cam sensors are new. I've got a vacuum pump but not the right connector.