Where is the thermostat located on a 1990 Acura Integra?

Remove the air intake tubing from the throttle body. Find the lower radiator hose, and follow it to where it connects to the engine which will be just above the starter. The thermostat is behind the elbow that the hose is connected to - unbolt the 2 or 3 bolts that hold the elbow to the engine and it should come right out.