Site hosted by Build your free website today!


A  B  C  D  E  F  G  H  I
 J  K  L  M  N  O  P  Q
R  S  T  U  V  W  X  Y  Z

Ia   Id   Ig   Im   In    Int

Ideal Air/Fuel Ratio A term used for Stoichiometric air/fuel ratio.

Idiot Light
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.

Idle Mixture The mixture of air and fuel (usually about 14:1) 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


[1] 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.

[2] 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.

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

[1] The pulley in a rear derailleur that stays farthest from the freewheelcogs and functions to keep tension on the chain of a bicycle.

[2] A small pulley located about half way from the front to back of a long chain such as found on a tandem bicycle.

[3] 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

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 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 Tracking Switch  (ITS) used on CFI vehicle to inform the EEC if the throttle is in contact with the DC motor

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

Ignition The firing of a spark plug to ignite the air/fuel mixture in the combustion chamber.

Ignition Box  A product that will increase the voltage to a vehicle's coil, which in turn provides the engine with increased spark energy.

This helps produce a more complete burn of the air and fuel mixture, for both more power and better fuel economy. Many ignition boxes also provide multiple sparks, instead of firing just once per cycle, which also is designed to create a more complete burn. Additional benefits of an ignition box include quicker throttle response, smoother idling and starting, and reduced emissions.


Ignition Circuit An ignition circuit is made up of two sub-circuits: the primary, which carries low voltage; and the secondary, which carries high voltage. The primary circuit is controlled by the ignition key. It releases 12 volts of electricity from the battery or alternator through the coil to a set of breaker points in the lower part of the distributor, or to the relay in electronic ignition applications. When the points or relay are closed, current flows through the chassis back to the battery, completing the circuit. When the points or relay are open, the flow stops, causing a high-voltage surge to pass from the coil through a rotor in the top of the distributor to the spark plugs. Once the car has started, the voltage regulator protects the battery from being overcharged by the alternator. part of the low -voltage current is absorbed by the condenser when the points are open.

Ignition Coil  A pulse transformer which is a part of the ignition system. It receives a small amount of electrical voltage from the battery and steps up the low "primary" voltage and amplifies it into a big jolt of voltage of about 20,000 volts, and sends it to the spark plugs via the distributor. It is made of two windings and a core of iron. The primary coil has about 200 turns of relatively heavy wire. The secondary windings may have as much as 22,000 windings of fine wire. As electricity travels through the primary winding, it produces a magnetic field in the coil. When the points open, the magnetic field collapses and the movement of the magnetic field induces current in the secondary windings of the coil. The voltage is stepped up in proportion to the ratio of secondary to primary turns and the distributor directs this high voltage to the spark plug. Also called just "coil."

Ignition Switch A five-position switch that is the power distribution point for most of the vehicle's primary electrical systems. The spring-loaded START position provides momentary contact and automatically moves to the RUN position when the key is released. The other switch detent positions are ACCESSORIES, LOCK, and OFF.

Ignition System The various components that provide the spark to ignite the air and fuel mixture in an engine during the combustion process. Some late-model engines (and virtually all vintage engines) use a distributor to tell the coil when to fire. Many late-model vehicles feature a distributorless ignition system, in which case the engine management computer tells the coil when to fire. The spark energy then passes through the spark plug wires to the spark plugs.

Many people enhance the performance of an ignition system by adding an ignition box and a high-performance coil, or even swapping to higher-performance spark plugs.

Ignition Temperature The lowest temperature at which a combustible material will ignite and continue to burn independent of the heat source.

Ignition Timing  The moment at which the spark plug fires, usually expressed in the number of crankshaft degrees before the piston reaches the top of its stroke.

Ignition Wire  See spark plug wire.


[1] A rotating member of a centrifugal pump which is equipped with vanes to convert mechanical energy into fluid energy. A rotor or wheel with blades or vanes used in pumps to drive and circulate fluid. Also see volute.
[2] A fluid coupling or torque converter - the driving member connected to the crankshaft via drive plate and converter cover which generates the fluid flow inside the converter. The driving torus in the fluid coupling or torque converter of an automatic transmission.

Independent Front Suspension

(IFS) A suspension system where the two front wheels are sprung independently from each other. It has the advantage over a beam axle suspension because it allows the engine to be positioned further forward and lower between the wheels. In this way there is more room for the passengers, the position of the hood is lower, the vehicle has a lower center of gravity, and the unsprung weight is reduced. When the front wheels are not independently sprung, there is some caster wobble and shimmy that make it difficult to hold on to the steering wheel.

There are several styles of IFS, including designs that use coil springs and designs that feature torsion bars.

Independent Rear Suspension  Abbreviated IRS. A type of rear suspension system in which each wheel and tire operate independently of the other for better traction in tough conditions. This design also reduces body roll, as well as a vehicle's tendency to squat down in the rear when accelerating or leaning forward when braking. By keeping the vehicle's weight better balanced, IRS improves both ride quality and handling--and safety. Very few vehicles come with IRS (Corvettes and Jaguars are among those that do), but it is possible to retrofit IRS to some cars and trucks.

Independent Suspension  Suspension in which each wheel is sprung individually so that any disturbance on the wheel has no effect on the opposite wheel.

Induction  The way an engine takes in air and fuel. A turbocharger or supercharger can be used to create a forced induction system, which can take in more air and fuel than a naturally aspirated system.

Induction System 
See intake system.
See also induction.

Inertia  That force which tends to keep a stationary object from being moved, and tends to keep a moving object in motion. Some effort is needed to get the object moving if it is stopped, and to stop an object if it is moving.

Inlet Manifold  British term for intake manifold

Inlet Valve British term for intake valve.

Inline Engine  In-line Engine

An engine in which all the cylinders (usually three or more) are arranged in a straight row (either vertically or slanted). The pistons drive a common crankshaft.

Also called a "straight engine."

An inline 4 cylinder engine

Input Shaft The shaft delivering power into a mechanism. The shaft from the clutch into the transmission is the transmission input shaft. Also called clutch shaft. Also see gearbox input shaft and transmission input shaft

Intake Manifold The connecting tubes between the base of the carburetor and the port openings to the intake valve or intake ports. The air-fuel mixture travels from the throttle body into a chamber called the plenum which feeds individual tubes (called runners) which lead to the individual intake port. Its purpose is to transfer the air-fuel mixture to each cylinder. It is usually an aluminium casting or a GRP molding, with one intake opening and as many outlets as there are cylinders in the engine.

Also called "inlet pipe." 
British term is "inlet manifold."

Also see 

ram intake manifold 
variable intake manifold 

Intake Stroke The first stroke is called the intake stroke. The piston moves down the cylinder, creating a partial vacuum in the cylinder. A mixture of air and fuel is then forced through the inlet valve into the cylinder by atmospheric pressure, now greater than the pressure in the cylinder. The exhaust valve stays closed during the stroke.

Intake System The various components that deliver air to a late-model engine. Air generally flows through an air box and air filter, then through ducting to the throttle body, and on through the intake manifold to the cylinder head (or heads). Many people install less restrictive intake system components to improve a vehicle's performance and often its fuel economy. Another way to enhance performance is to swap to a cold air intake system.

Intake Valve  A valve in a cylinder head that opens to allow air and fuel into a combustion chamber. Part of a vehicle's valvetrain.

Internal-Combustion Engine  Any engine, either reciprocating or rotary, in which the fuel is consumed in the interior of the engine rather than outside of the engine.

Explore How The Internal Combustion Engine in Your Vehicle Works


A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z

Main Menu


Click the arrow above to go back where you just linked from


Contact Us

The objective of this Web Page is to familiarize you with basic auto maintenance
-  in some common emergencies -
not to make you an expert in auto mechanics

DISCLAIMER: PLEASE READ - By printing, downloading, or using you agree to our full terms. Review the full terms by clicking here. Below is a summary of some of the terms. If you do not agree to the full terms, do not use the information. We are only publishers of this material, not authors. Information may have errors or be outdated. Some information is from historical sources or represents opinions of the author. It is for research purposes only. The information is "AS IS", "WITH ALL FAULTS". User assumes all risk of use, damage, or injury. You agree that we have no liability for any damages. We are not liable for any consequential, incidental, indirect, or special damages. You indemnify us for claims caused by you.

  I am in no way, shape, or form telling you to do this yourself. Your results may vary. If something goes wrong, it is not my fault!
These are just guidelines.

Copyright © 2000 Jon's

Images, Inc. All rights reserved