96 aurora high idle

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

006 Idle Speed Problems Idle Speed Wrong Do you have a professional type scan tool ? If not ,take it to a qualified repair shop .
007 Idle Speed Problems Scan Data for Idle

It is usually caused by the air leakage in the intake manifold. Check the following:
1. Check all the vacuum hoses from around the throttle body.
2. Under the throttle body there are three rubber hoses. Two pipes are of the same size and are used for the coolant circulation through the idle air control valve and the third one is a bit thicker than the two. It is used as the air release tube for the idle air control valve, (if the valve is separate from the throttle body). If the idle air control valve is separate type, it is attached to the side of the surge tank, other wise it is fixed to under the throttle body with Philips type screws (4 mm) as a single unit.
3. To locate the intake air leaking source, take a vacant mineral water bottle, fill it with tap water, make a small hole on the cap with a bag sewing needle, invert it and spray water by pressing the bottle with little pressure and pointing it towards a suspected area. If there is any air leaking from around the intake manifold it will produce an audible suction noise. Locate the area and fix it.
4. Remove the idle air control valve, clean and free it up and install it back.

yes it has a idle air control motor try cleaning it or replace

High idle
Changed IAC still the same, shown on scanner IAC 50-60 %, if it set to 40% the Idle is ok. What cause the PCM to set IAC too high? Is any one know?

The Idle Air Control valve is located on the throttle body. If you follow the intake tube from your air filter all the way back to the intake manifold, where the intake tube connects to is the throttle body. Remove the intake tubing and you can see the throttle body.

There are two sensors on the throttle body and a vacuum line. You'll see two harnesses going to the throttle body, one is the IAC.

However, a quick diagnostic check can be done without touching the throttle body to confirm your problem. If the car has a normal idle when initially started but then rises to a higher idle and stays there BUT then if you were to shut the car off and restart it and it comes back to normal that is the Throttle Position Sensor (TPS). This is also located on the throttle body (the other sensor to the IAC). If it is the IAC it will be high and maybe fluctuate a bit.

The throttle body is where the carburetor used to be, in the middle top of the intake manifold where the air intake tube ends.
Use a major brand "Fuel throttle body cleaner" in your gas tank every 6 months or so. Don't use store brand. Ther eis also a spray for the linkage, etc. Use that too... and spray into the throttle body with engine running. Don't let the engine die while spraying into the throttle body.

If you have a high idle and lunging...that usually happens when there is a leak on the intake manifold side allowing more air to get in, then the computer senses the increase in air and adds more fuel. There in turn has to be one more failure in the system to allow the idle to run away, may be a tps sensor (throttle position sensor) or something down the line.

Check for cracked vacuum hoses in your engine bay. Especially on your intake manifold.

Most likely the throttle body gasket (between the throttle body and the intake manifold) is leaking.