Engine vacuum leak.
The IAC valve is just that...The Idle Air Control Valve. It is responsible for keeping the idle at set parameters. And yes, it can make the engine idle at high RPM.
Most common high idle issues are leaks in the vacuum system.
No, on a fuel injected engine it can cause high idle speed.
To adjust the idle on a 1995 Chevrolet S10 with a 2.2 liter engine, locate the Idle Air Control (IAC) valve, which is usually located on or near the throttle body. Use a flathead screwdriver to turn the adjustment screw on the IAC valve to increase or decrease the idle speed. Make small adjustments and test the idle speed by running the engine to ensure it is at the desired RPM.
Engine coolant temp circuit high input. The engine coolant temp sensor make be bad.
Cars often idle fast when you start them up. The automatic choke will make the car idles fast for a while then the idle speed will slow down, once the engine warms up.
The knock sensor is a passive device that has no effect on engine idle.
Could be many reasons for that condition. Be more specific including the year, make, model and engine info.
This question is not answerable without make model year and control system for the engine.
It wouldn't make much of a vacuum leak to cause the engine to idle at high RPM. First check for vacuum leaks even though you may still have good manifold vacuum.
No , according to the Gates website ( they make timing belts etc. ) the 1.9 liter engine in a 1996 Mercury Tracer is NOT an interference engine