Cadillac Repair: Cadillac sts 1999, cadillac seville, cadillac sts

Question
Hello, I have a 1999 cadillac seville sts my check enigine light comes on every once and awhile and when its on my temp gauge jumps all over the place and my rpms sometimes goes really low.  Now my light is on all the time since i let it sit over winter and the temp gause still jumps around or stays on the cold, also black smoke pores out the exuast when the rpms act up.  is there a way to do my own dignostic check on this year.......  What do i do.

Answer
Sounds like a classic fault of the COOLANT sensor that needs to be replaced. Also the spark plugs need to be replaced or cleaned and the computer needs to be CLEARED of the code. You will need, If necessary, Electrical schematics and picture locations of the components within the system that is causing you problems of which can't be done on this website which only allows one picture.  I do not have a website so you will have to e-mail: onlineautohelp@msn.com in order to obtain the information.