Dictionary of Automotive Terms Abbreviations

DICTIONARY OF AUTOMOTIVE TERMS - "Id"

ID: Acronym for inside diameter.

Ideal air-fuel ratio: See
Stoichiometric ratio

Identical part: See
Shared component

Identification: See
Engine identification number
Program comparison and identification

Identification color

A particular color for a specific amperage of fuse.
A color scheme for wiring

Identification number: See
Engine identification number
Vehicle Identification Number

Identification plate: Provides information such as manufacturer, part number, and specifications. Frequently mounted on the outside housing of motors and compressors.

IDI: Acronym for integrated direct ignition system

Idiot box: Trucker slang for a T.V. set as in "When I get home I'm gonna buy me a new idiot box."

Idiot light: See
Idiot lights.

Idiot lights: A colloquial term for the indicator lights on the Dashboard which are illuminated when the vehicle is experiencing some problem such as a lack of oil, overheating, failed brakes, low fuel, etc. The alternative is to install gauges which indicate the level of fluids and temperature. A combination of both gauges and lights is ideal.

IDL: Acronym for Idle Position Switch

Idle

The Engine speed when the vehicle is not moving. The engine's slowest practical speed.
A running engine without added throttle pressure while the vehicle is stationary.

Also See
Fast idle
Fast idle cam
Fast idle screw
Fast idle solenoid
Tick over

Idle air bleed screw: A screw found on some Carburetors which allows air to enter the Carburetor when the throttle is closed, so that the vehicle can Idle. It also prevents the formation of deposits in the throttle area. The adjustment of this screw is part of a basic Tune-up.

Also See
Bleed screw

Idle air control valve (IAC)

On a fuel injection vehicle, a valve that allows air to bypass the throttle plate(s), increasing idle speed. The valve is operated by an electric solenoid or motor. The vehicle computer controls the amount of opening to regulate idle speed for varying conditions such as cold string and air conditioner compressor load
An electronically controlled device that controls idle speed on fuel injected vehicles by controlling bypass air.

Idle air jet: A hole in a fixed-jet carburetor through which air is drawn into the idle system

Idle air stabilzation valve: Electronically controlled valve used to maintain idle speed at a predtermined level

Idle cam: See
Fast idle cam

Idle capacity: The component of operable capacity that is not in operation and not under active repair, but capable of being placed in operation within 30 days; and capacity not in operation but under active repair that can be completed within 90 days.

Idle channel restriction: Used on carbureted vehicle. Does the same thing as the idle feed restriction, but is located in the idle passage just below the idle air bleed instead of the bottom of the idle tube. In the primary idle channel, the amount of fuel emitted by the idle discharge port is adjustable because there is a screw with a tapered tip extending into the port. On the secondary side, the idle discharge port uses a fixed idle channel restriction with no adjustment

Idle circuit: At Idle and low Speeds, the Carburetor system supplies enough fuel to the engine to keep it running. When the vehicle gets up to Speed (usually about 24 kph or 15 mph) the idle circuit kicks out of operation so that fuel is supplied by the main metering system. Also called the low-speed circuit.

Idle discharge hole: Used on carbureted vehicle. The hole through which the idle mixture enters the airstream flowing past the throttle plate. Also called curb-idle port

Idle feed restriction: Used on carbureted vehicle. A metering orifice that controls the amount of fuel that can enter the idle tube. Also called idle orifice or idle jet.

Idle jet: A carburetor jet within the idle system which supplies a constant amount of fuel for the formation of the idle mixture

Idle limiter: Any device that limits the maximum richness of the idle air/fuel mixture in the carburetor. Also aids in preventing overly rich idle adjustments. Limiters take either of the two following forms And external plastic cap or a internal-needle type located in the idle passages of the carburetor

Idle limiter cap: An external plastic cap on the head of the idle mixture adjustment screw to maintain preset emissions levels and prevent unauthorized tampering

Idle mixture: The mixture of air and fuel (usually about 141) being fed to the Cylinders.

Idle mixture adjustment screw: See
Idle mixture screw

Idle mixture screw: A tapered screw located on the outside of the Carburetor which controls the proportion of the Fuel-air mixture. It is now illegal to adjust these if limiter caps are present. If you turn the screw clockwise, the mixture will be leaner while turning it the other way results in a richer mixture.

Idle orifice: The idle restriction tube or idle jet

Idle power: The system rate of doing work when only the minimum work rate is employed by the system.

Idler

A gearwheel between a driving and a driven gear in a gear train which may serve to reverse the original direction of rotation of the driven wheel.
A free-turning pulley or wheel which serves to maintain tension in a belt drive.

Also See
Reverse idler gear

Idler arm: In a parallel relay-type Steering linkage, it is one of the connecting levers. The steering Gearbox is attached to a Pitman arm which converts rotary motion to lateral motion. The pitman arm connects to a transverse centerlink which connects to the idler arm attached to the Frame side rail on the opposite side of the vehicle. The ends of the centerlink connect to two adjustable Tie rods that transmit the lateral movement of the centerlink to the Steering arms at each Steering knuckle.

Idle regulation electrovalve: located in the throttle flap bypass circuit, it compensates for engine rpm drop when the air conditioning compressor or other engine loads are operated.

Idler gear: A gear that is placed between two other gears to reverse the direction of rotation of the output gear.

Also See
Reverse idler gear

Idler pulley

The Pulley in a rear Derailleur that stays farthest from the Freewheel Cogs and functions to keep tension on the Chain of a Bicycle.
A small pulley located about half way from the front to back of a long chain such as found on a tandem bicycle.
A spring-loaded pulley designed to maintain the tension of the timing belt or a cam chain.

Idle screw: See
Fast idle screw

Idle solenoid: See
Fast idle solenoid

Idle speed: This is the Speed of the engine with the following conditions The Transmission is in Neutral (or park in Automatic transmissions), the engine is fully warmed up, the Choke butterfly is fully open, and there is no extra Accessories in operation (i.e., Air conditioner, radio, lights). Also called idling speed

Idle speed actuator: An electronically-controlled air bypass around the throttle. Also called Idle-speed stabilizer or a Constant idle system

Idle speed adjustment: The alteration of the engine idle speed.

Idle speed control (ISC)

Maintains the idle speed of the engine at a minimum level. There are currently two types of computer controlled idle speed control DC motor ISC and air bypass ISC
An electronically controlled device that maintains idle speed on vehicles by controlling throttle position at idle.

Idle speed control motor: (ISC) and ECM controlled motor that extends or retracts a plunger that contacts the throttle level, which regulates the position of the throttle valve to compensate for an additional load, such as the air conditioner, power steering pump, etc. On the engine. Although it regulates idle speed, it is not used to adjust the curb idle speed. ISC motors are commonly used on carbureted and throttle body injected (TBI) vehicles

Idle speed screw: A screw located at the bottom of the Carburetor on the outside which keeps the throttle from closing completely when the vehicle is idling and thus controls the Idle speed. This is adjusted as part of a basic Tune-up.

Idle speed stabilizer: A device which ensures steady engine rpm at idle speed. An electronically-controlled air bypass around the throttle. Also called Idle speed actuator or a Constant idle system

Idle stabilizer valve: A device used to control the amount of air for engine operation at idle. It consists of a rotary valve connected to an armature. During normal operation, a duty cycle is applied to the armature by the ECU. This causes the valve to rotate in a direction opposite to spring tension. Lengthening or shortening the electrical pulses of the duty cycle causes the opening for the bypass air to become larger or smaller, resulting in the idle speed rising or falling accordingly. When no current is applied to the rotary valve, it is pressed by spring pressure against a stop and maintains a specific air gap. This will allow the engine to idle, if the stabilizer fails.

Idle stop solenoid: A small Cylinder located on the outside of the Carburetor on some cars. It prevents the vehicle from continuing to Idle after the Ignition switch has been shut off (i.e., Dieseling). The position of the striker rod in the Cylinder can be adjusted in a Tune-up to the correct Specifications.

Idle stop valve: A solenoid-operated valve which cuts off fuel in the idle system of a carburetor and so stops the engine from running-on when the ignition is switched off

Idle system: At idle speed, the throttle valve is closed to such an extent that the airflow underneath the plunger no longer forms a sufficient vacuum; the fuel is then supplied via an auxiliary system, the idle system, which consists of the idle jet, the idle air jet, and the mixture control screw

Idle time: The time when a system is capable of but not producing power; startup time

Idle tracking switch: (ITS) used on CFI vehicle to inform the EEC if the throttle is in contact with the DC motor

Idle transfer port: A port drilled into the carburetor body slightly above the idle port to allow extra fuel/air emulsion into the airstream during the transition period when the throttle plate is opening from its idle (closed) position to a larger (cruising) opening angle. Also called idle transfer slot

Idle transfer slot: A port drilled into the carburetor body slightly above the idle port to allow extra fuel/air emulsion into the airstream during the transition period when the throttle plate is opening from its idle (closed) position to a larger (cruising) opening angle. Also called idle transfer port

Idle vacuum valve: (IVV) used in conjunction with other vacuum controls to dump air injection system air during extended periods of idle, to protect the catalyst

Idling: The action of an engine as it turns over at low speed with minimum throttle.

Also See
Sonic idling

Idling circuit: The passages, jets, etc. in a fixed-jet carburetor which provide idling mixture to the carburetor barrel

Idling drag: The forward motion of a vehicle with automatic transmission, with engine at idle and selector lever in position D (Drive). Also called creep

Idling speed: See
Idle speed

IDM

Acronym for Ignition Diagnostic Monitor
Acronym for Injector Driver Module