It is very easy to access in the left hand valve cover near the oil fill opening. This is the valve cover closer to the radiator.
If you pull it up, it will slide out.
The idle air control valve is located on the throttle body, and the EGR valve is located on the intake manifold.
1991 Corsica its under the trottle body
For a 1991 Chevrolet Corsica : My Chilton's Auto Repair Manual shows : ( 15.6 U.S. gallons )
It doesn't have one, it is distributorless.
13.6 gallons
Green coolant (prestone, etc)
You have to take the door apart
Depends on which engine it has. Try a Google Search.
16.5 to 17.1 gal
Pass side valve cover.
Remove the wiring harness from the back of your 1991 Chevy Corsica turn signal. Remove the turn signal retaining bolts. The entire turn signal will come out. Reverse the process to install the new turn signal.
As soon as you pop the hood, it should be to the left of the engine. it is visible from top view.