MY 1999 LUMINA ACCELERATES MOST OF THE TIME WHEN TURNED ON. I HAVE TO TURN IT ON AND OFF UNTIL IT STOPS.

Sounds like the auto throttle is jammed or the throttle pedal is jammed. Try pushing on the gas pedal a few times to see if it frees.

Check the belt tensioner

Since you changed the sensor we will assume it is working. When you disconnect it you put the computer in limp mode which stops it from using sensor values. If code 300 is the only code we will assume the coolant temp sensor and others are ok.
I would check fuel pressure with a gauge next.

seems your electronic controled EGR is failling, this happens after you drive over 45mph for a few miles and then coming to a complete stop. this is the most common failure it may turn your check engine lite on but next time you start the car it will be off until it dies again. good luck

sounds like a dead battery

Turn key to on, let the light flash till it stops (usually 10-15minutes) and remains steady on. then re-start the car. If this does not work, try it three times. If still no luck the problem is likely the ignition lock sensor or the module, most often the tumbler

I was having similar issues with my '95 Lumina. It started out with the passenger side brake light not working and the turn signal switch on the column acting funny.
Eventually, someone pulled-up next to me and told me that I had no rear lights at all.
It turned out to be the turn signal switch in the sterring column.
Hope this helps.

because aaa can jump start it and you can't sounds like maybe the battery cables are curroided (dirty)
in-between the battery post and the clamps, clean the battery terminals and charge your battery as a loose conection can run down even a new battery

no fan comes on when engine cold start up .but it will come on when you turn on air conditioning or defrost on .if engine idling a while when temp get 190 degree the fan will kick on.if over heating you got air in system .wait until cools check coolant add more .crank engine let it idle few. minutes when start warming up turn off engine wait a while before removing radiator cap so you wont get scald.add more coolant .crank it again starting warming up turn off engine wait a while .add coolant .keep doing this procedure until your coolant stop dropping off .if you do this more than 6 times you got a leak some where.check crank level for signs.if oil level higher than normal.if everything looking good.when engine cool make sure add coolant to over flow jug cold level mark.

Check em one at a time. try this first. It is trial and era.