1997 ford Taurus wagon has intermittent speedometer and tachometer drop but not to 0

I have had check engine lite come on and go off by itself for about a year, code is O2 sensor bank 2. Then my son used the car while visiting and reported that the speedometer dropped to around 20 -30 when he was doing 60 MPH on a 50 mile trip but it only happened once and he returned the car and I parked it for a few weeks since I use another car most of the time. Then I had to use it and drove about 35 miles and the same thing happened to me and I also noticed that the Tack also dropped to about 1000 RPM at the same time. It also seemed like the gas peddle did not respond properly and almost like the cruse control was cutting in and out. I stopped and turned off the car for about 5 minutes and restarted with everything working just fine! The code now in the computer is P0430 but no check engine light on. I have not driven it again since then.