IDLE PROBLEM... WHEN I TURN ON MY CAR FOR THE FIRST TIME IN THE DAY IT REVS AT 4K RPMS THEN WHEN ITS WARM UP IT DROPS SLOWLY TO 2K RPMS.. CHANGED IDLE SENSOR AND STILL DOING THE SAME THING. 1990 CIVIC SI MOTOR( ZC VTEC SOHC)

have vechicle code scan could have faulty idle air control valve.

Sounds like the idle control valve. The same thing happened to my Mustang and that was my problem.

idle air control valve is bad replace it. at start up choke control runs till warm up while driving throttle opening controls engine at idle ,the idle air control valve.

try to reset the computer if that doesnt work reset the idle speed it may have picked up bad codes

This is very likely your idle air control valve. Common problems with ford motors in my experience.

Check for vacuum hose leaks or component clogs. You can use vacuum pressure tester.
or turn the idle screw down.

The pcv hose connector at the rear of the intake may have cracked causing a vacuum leak.

Check the spring on the throttle body. could be something to do with it.

Look at your air intake on the motor: as the pedal is pushed you'll see the apparatus and a screw that controls how far back the pedal goes when it's not being pushed. The easiest way is to see the idle adjusted and more fixes for the idle problems are available on YouTube and through a Google search.

I've got Hyundai Lantra 1.6 year 2000. It's take time to start when it's hot. When I start my car it revs at about 2k-3k rpm. It also does it when I come to a stop. When I come to a stop it will stay at a higher rpm than that of idle speed. It drives ok when on freeway but uses more petrol. I have changed the water & petrol pump but no luck