When you start your 1987 Honda accord the rpms instantly rise what causes that?

Answer 1

That is the Fast Idle action required for smooth running while the engine is warming up. On the carbureted (DX) model, a fast idle cam props open the throttle when the engine is cold, raising the idle. The cam is controlled by the thermostatic spring which also controls choke position, the spring is heated by an electric heating element when the car is started and gradually reduces choke and idle. Additionally, at several temperature thresholds, thermally controlled valves apply vacuum to diaphragm-type actuators to reduce idle speed and choke more quickly than the thermostatic spring alone. On the fuel-injected (LX, LX-i) models, fast idle is controlled by the fast idle valve which shunts air around the throttle, giving the same effect as opening the throttle. The fast idle valve is a wax-type valve similar to the cooling system thermostat and is arranged to provide maximum air when cold and none when fully warmed up (is warmed by passages through which engine coolant flows). By way of the engine's other various sensors the computer (ECU) is informed of the increased airflow and adds more fuel via the injectors to maintain correct fuel-air ratio during fast idle. Drew