1996 Jeep Laredo check engine light

When I drive my cherokee and the car warms up as I come to a light the oil pressure gauge goes down & the
check engine light comes on. Then when I begin to go again the oil pressure guage goes back to normal & the lights go out again. This happens everytime the RPMs go
down by stopping. I checked the oil--it is good.I checked the transmission--its good. Could it be a bad sensor or what is your opinion. Thanks

P.S. There are two check engine lights. The Orange light is the one that comes on. Thanks again