2004 hilux 3rz engine idles 1200 rpm

if no vacuum leaks...replace the idle air control valve

Proper idle speed for this vehicle about 800 RPM; 1200-1400 RPM is indeed too high. This usually occurs due to too much air entering the intake manifold. Air flow during idle is typically controlled by an idle air control (IAC) valve or in newer vehicles (as in this case) an electronic throttle body. The throttle body could be physically binding which could keep the throttle blade open too much. Cleaning the throttle bore and blade is a good first step, but a special function called the "ECM/PCM idle learn procedure" must be performed with an advanced diagnostic scan tool after this repair. Another possible cause for receiving too much air into the intake manifold is a vacuum leak. Vacuum leaks can originate from any area exposed to engine vacuum including the PCV valve, PCV hose, EVAP canister purge valve, throttle body, intake manifold, brake booster hose and brake booster. A diagnostic scan tool capable of viewing live data is a great way to check for vacuum leaks by watching the fuel trim values; if a vacuum leak is present, the computer will be adding extra fuel to maintain the correct air/fuel ratio. Lastly I do want to mention that the idle speed is adjusted higher when the steering wheel is turned or the A/C is turned on. These signals are sent to the ECM from the A/C pressure sensor and power steering pressure (PSP) switch however I've never personally seen either one cause a high-idle concern. You can read more here: https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-ac-high-pressure-hose

check hoses for vacuum leaks also throttle body may need to be cleaned and or throttle body position sensor can be starting to be faulty or may require cleaning with throttle body --the following links show how to clean a throttle body look up the ones that do it in /on vehicle you dont have to remove it from vehicle
How to Clean throttle body GM 3800 throttle Body Tune Up Cable accelerator... Throttle body cleaning and idle relearn procedure

If the car has not ran very long since you did the cleaning it might be excess throttle body cleaner in the intake manifold. Otherwise, your is with the throttle body. The throttle body controls the air to the engine, the computer controls its position and everything else in the air/fuel mixture. I would double check to make sure that the throttle body is closing completely. If that is not the problem, I would look for either a leaking gasket or a hole in the system somewhere between the throttle body and the engine. Because if you are getting too much air to the engine, the computer will think that is the rpm that it is supposed to be running, and it will give the engine fuel to burn the air.

Find out what the trouble codes are before you replace anything.
I would disconnect the idle air control valve when the idle speed is around 1200 and see if the idle speed stays or continues to climb.
if it climbs with the valve unplugged, you have a vac leak somewhere, probably the intake gasket.

In most cases problems with idle speed involve the idle air control valve or a dirty throttle body. The computer controls idle speed by how much air is allowed into the intake thru the control valve.
If the throttle is not sticking, I would check the valve and the bore of the throttle body.
You could also have a vac leak but that would usually be a constant problem.

Usually when the engine is "hunting" for the idle speed, the throttle position sensor or idle air control valve is faulty, or there is gunk in the throttle body, or a vac leak somewhere.
The computer controls the idle speed by using that control valve.
Is the check engine light on when the engine is running ?

Do you perhaps have a small exhaust leak? Check ahead of the O2 sensor. If the exhaust can **** fresh air in it can't give the computer an accurate reading and the engine will rev up and down at idle. Hope this helps.

You could have a simple vacuum leak or a faulty computer.Listen to the engine with the hood up to see if you can hear a loud hissing sound that indicate a vac leak

Make sure your throttle cable is not bound up on anything. Also where the throttle cable ends at the throttle body make sure it moves freely and there is nothing obstructing its movement..Rpms are a little too high to be a vacuum leak.