WHY DOES MY 1998 OLDS BRAVADA HAVE A REALLY ROUGH IDLE AT START UP ?

There are many possibilities, but if I had to guess, I would suspect you have a vacuum leak causing lean fuel trim codes...bascially the engine takes in too much air compared to the fuel it is supplying. Can cause rough running. On the other hand, you could have a misfire from tune up related items. A good diagnosis is in order to give you direction. Good luck.

go to autozone get ck code for free it brobley carbon in egr valve autozone makes a gasket with a screen in it so it wont get carbon syuck in valve