Engine Maintenance and Modification Bradley Artigue

FIAT 124 Spider
Engine Maintenance + Modification
5.4 Warm-Up Components
The warm up phase starts when the thermo-time switch heats up and closes the cold
start injector. The engine temperature sensor, located in the water coolant “T” in front
of the cylinder head, sends coolant temperature readings to the fuel injection computer.
The engine is still cool enough to have increased frictional resistance and, without
additional fuel and an increased idle speed, will stop running. To compensate the fuel
injection computer turns on a device called an auxiliary air regulator. This device allows
air to be drawn directly into the plenum, bypassing the throttle plate. The effect is an
increase in idle speed – the computer will give the engine more fuel to create an
appropriate ratio to the inbound air. Once engine temperatures reach the normal
operating range the auxiliary air valve closes. The engine now enters a “normal”
operating phase, with no cold or warm up devices operating.
Figure 35: Warm-up Operation in the Bosch L-Jetronic System
5.5 Idle Speed Control Components
Your FIAT fuel injection system maintains idle by allowing a small amount of air to
bypass the throttle plate and enter the throttle body. This amount of air is controlled in
three ways. First, the mixture is statically controlled by turning a bypass screw on the air
flow meter body. Next, the air strikes the throttle plate, which at rest is open
approximately 1 degree and allows a small amount of air into the plenum. Additional
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