the car:1992 Eldorado 4.9 v8 automatic transmission

ok so just recently my caddy started actin very funny it will run very smooth and then just out of nowhere(sitting in driveway going down road it just picks its times to act up) it will begin to run very very rough it will begin missing very bad and surging idle from 800 to 2000rpm when it begin to do this the monitoring system will pop up and say set timing mode it will also say engine temp hot but here is where it gets intresting it will only say these things when it begins to run rough and when you check the info on the dash the temp reads 304 deg F(i know for fact the motor was nowhere near this hot i could touch my hand to the top of it and it was relativley warm not hot) then it will go away to 2 lines -- just like that and pop back up a completely random number it acually said -34 deg f right after it said 304 it will also say set timing mode also the check engine light will flicker on and off and sometimes stay but just as soon as all this starts it will go away on its own and go back to running perfectly the temp goes back to its normal 180 to 190 deg the set timing mode will go away and everything is fine just like its a new car

does anybody know what this is caused by? i am completely stumpped ive never seen a car act this way and it baffles me ive shook every wire i could find on the car as last hope with no changes could a sensor do this? seems like to many problems at 1 time for it to be 1 sensor?

please guys any help i will be very grateful for