There are three general types of two cycle induction. The most simple type of air intake induction is called a piston port engine. This type of two stroke engine has holes cut through the cylinder walls in specific areas. The second type of induction, and the most popular type, is reed block induction. This consists of multiple reed petals that allow air into the crankcase and keep it trapped there. The third type of two stroke induction is generally used in rotax two cylinder engines is the rotary valve engine. It does slightly better than reed engine because there is no restriction from reed petals. The rotary valve rotates past the crankcase intake port at a specific time to allow air through then seal the air into the crankcase.
Does your car idle rough or the speed cycle up and down. You probably have a bad idle air control valve. The only purpose of the idle air control valve is to keep the engine’s idle smooth. The engine’s computer gives the idle air control valve the feedback it needs to hold a constant rpm. The idle will be around 1000 rpm’s when not in gear and around 800 rpm’s in gear. This iac valve is on a Nissan Maxima and is similar to most idle air control valves.
A rotary valve engine is always a two stroke engine. Most rotary valve engines are rotax engines. Although other rotary engines such as suzuki and kawasaki have been made. Rotax engines are used in snowmobiles, jet-skis and motorcycles and aircraft engines. A rotary valve refers to the intake of a two stroke engine. There are three types of intake designs for two stroke engines. Simplistic two strokes are piston port, meaning that the piston movement past the port controls the incoming air timing. The piston port engine doesn’t do a very good job of keeping the airflow to stay in the engine. The air can simply travel back out of the engine. The most popular intake air induction is the reed port engine. It uses reed petals to allow the intake air in the engine and traps it there. The tension of the reed petals can change with the use of different petals and can provide some power improvement at certain rpm ranges. A rotary valve engine has the best intake air control.
The idle air control is a control system used on fuel injected cars. The idle air control or IAC valve controls the idle speed of the engine. The IAC valve is controlled by the ECM (computer). The computer gets it’s information from the rpm which is supplied by the distributor, crank or cam sensor. The IAC valve moves in and out to bleed air behind the throttle plate. This air bleeding is the same as opening the throttle plate. The idle speed can be controlled precisely the throttle plate which isn’t controlled as well. Air conditioning will drop the idle speed down and will kill the engine if the IAC doesn’t work well. The idle air control will be located on the side of the throttle body. The IAC can become sticky after time and will cause the the engine to surge, rev or stall the engine. The valve can be removed and cleaned if not too severely worn. Usually the valve needs to be replaced. Make sure the gasket looks alright. Also make sure the idle air control is secured well and doesn’t leak air, or the engine will rev up.