Again the almighty raw potato comes in to play. Peel 1 - 2 large potatoes and add for 1/2 to 3/4 of an hour to absorb the burnt taste. You can also use a little sugar (to taste) to take the acrid burnt taste away.
Add fat, ie in the form of olive oil. The extra fat coats the tongue and therfore reduces the saltiness because the salt can't get to your tastewbuds!. This is the same theory behind eating dairy to...
If your spaghetti sauce tastes sour, it's because it's gone bad. Tomato sauce is acidic naturally but should never have a sour taste. My suggestions is to throw it away and make a fresh tomato sauce...