Radiator Glossary of Terms
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Idle Adjustment
Adjusting the engine idle speed. Idle is not adjustable on many late model engines with computerized idle speed controls.
Idle Air Control Valve (IAC)
An electrically-operated valve which allows air to bypass the throttle plate in a fuel injected engine to regulate engine idle speed.
Idle Limiter Cap
A plastic device pressed over a carburetor's idle mixture screw which limits the amount of adjustment available during service. Also designed to discourage tampering that could increase emissions.
I/M 240
Stands for "Inspection/Maintenance", an "enhanced" emissions testing program with a tailpipe test that lasts 240 seconds. The test is done on a dynamometer to simulate actual driving conditions. The vehicle is put through a "driving trace" as it accelerat
Idiot Light
A derogatory term for an instrument panel warning light. They're called idiot lights because they're for idiots who don't know how to read or understand gauges. Actually they're not all bad. An idiot light won't give you any indication that a problem is d
Idle Mixture
The air/fuel ratio that's delivered through the carburetor when the engine is idling. It can be adjusted by turning the idle mixture adjustment screw(s) on the carburetor. The screw opens up a little passage that lets more or less fuel into the engine. On
Idle Speed
This refers to how fast the engine runs when idling. It can usually be adjusted by turning a screw on the carburetor throttle linkage, or by turning an air bypass screw on a fuel injection throttle body. On many newer cars, however, it is computer-control
Idle Stop Solenoid
An electromagnetic device mounted on carburetor linkage that maintains the proper throttle opening for specified idle speed while the ignition is on, but allows the throttle to close farther when the ignition is switched off. This shuts off the engine's a
Idler Arm
A pivot point in a parallelogram steering system that follows the motions of the pitman arm. A worn idler arm bushing typically causes steering wander (looseness) and toe wear.
Ignition Coil
The component in the ignition system that turns low voltage into high voltage to fire the spark plugs. When 12-volts passes through the coil's primary windings, it creates a strong magnetic field. Then when the current is shut off (by the ignition module
Ignition Module
The electronic control for the ignition system. The module receives a signal from a magnetic pickup or Hall effect sensor in the distributor. The module uses this signal to open and close the ground circuit to the ignition coil to fire the spark plugs. Th
Ignition System
The various components that control the igniting of fuel in the engine's cylinders. The ignition system has two parts: the primary side (the distributor and electronic control module), and the secondary side (the ignition coil, distributor cap, rotor, spa
ILSAC
International Lubricant Standardization and Approval Committee.
Imbalance
The condition that exists when a tire's mass is not evenly distributed around the rolling axis and centerline, causing bounce (static imbalance) or shake (dynamic imbalance).
Included Angle
The sum of the camber and SAI angles in a front suspension. This angle is measured indirectly and is used primarily to diagnose bent suspension parts such as spindles and struts.
Independent Suspension
A suspension system that allows each wheel on a vehicle to move up and down independently of the other wheels.
Induction
A means of transferring electrical energy in the form of a magnetic field Principally used in the ignition coil to increase voltage.
Inflation Pressure
The pressure of air inside a tire that applies a tensile stress to the tire cords permitting them to carry the vehicle's load.
Inhibitor
A substance added to oil, water or gas to prevent foaming or rust.
Injector
A device that receives metered fuel under relatively low pressure and is activated to inject the fuel into the engine under relatively high pressure at a predetermined time.
Injector Rig Shear Stability Test
A test that specifically evaluates the permanent shear stability of multigrade lubricants.
Inline Filter
A filter which may be installed in a fuel line, power steering pump discharge line, or A/C compressor discharge line to trap debris that might cause damage.
Inner Or Inboard CV Joint
The CV joint closest to the transaxle in a front-wheel drive car.
Input Shaft
The shaft to which torque is applied, usually carrying the driving gear or gears.
Intake Manifold
A casting of passages or pipes used to conduct air or a fuel/air mixture to the cylinders.
Intercooler
A heat exchanger that's added to some turbocharged engines to cool the air after it leaves the turbo. This increases the air's density and means more air can be pumped into the engine. The result is roughly a 10 to 15 percent improvement in horsepower.
Intermediate Gear
Any of the gears in an automatic transmission between first and high gear.

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