The Exhaust Gas Recirculation (EGR) valve in your Isuzu Trooper is an exhaust intake regulator attached to the intake manifold of the engine. It operates by allowing a small measured amount of exhaust to enter the combustion chamber, thus reducing the temperature in the chamber. When the EGR valve remains open and allows too much exhaust to enter, it causes the temperature in the pistons to increase. This malfunction allows smog-forming emissions (nitrogen oxide) to enter the atmosphere. It's simple to replace the EGR valve.
Open the bonnet and locate the EGR valve. It's located on the left rear side of the engine and is attached to the intake manifold, near the firewall. Leave the battery plug in for now, but use precaution not to place any tools near the posts.
Unplug the single-prong electrical connection from the EGR valve. Disconnect the rubber vacuum tube and inspect these parts for excessive wear or cracking.
Remove the two EGR mounting bolts located on either side of the valve with a socket wrench. Use a hammer to gently tap the valve to break the seal. Remove the old EGR valve and scrape off the old gasket using a paint scraper. Be careful not to allow any debris to enter the chamber by stuffing it with a small clean towel.
Lightly coat the new gasket with a thin layer of gasket adhesive using your finger, then place it onto the manifold. Be certain the mounting bolt holes are properly aligned.
Carefully insert the new replacement EGR valve into the manifold opening. Secure the valve in place with the two mounting bolts. Reattach the rubber vacuum tube and the electrical connection.
Disconnect the battery to reset the engine check light indicator. Keep it disconnected for at least 4 hours before reconnecting it.
Reconnect the battery, start the engine and check to see if the check engine light remains off.
This repair should only be performed when the engine is cool to prevent being burnt by the manifold exhaust.