GM Corsica/Beretta 1988-1996 Repair Guide

General Information


The Model 700 throttle body system is used on 1988-91 2.0L and 2.2L engines.

The Throttle Body Injection (TBI) system is an electronic fuel metering system in which the amount of fuel delivered by the injector is determined by the Electronic Control Module (ECM). This small, on-board microcomputer monitors various engine and vehicle conditions to calculate the fuel delivery time (pulse width) of the injector. The fuel pulse may be modified by the ECM to account for special operating conditions, such as cranking, cold starting, altitude, acceleration and deceleration.

The TBI system provides a mean of fuel distribution for controlling exhaust emissions within legislation's limits. The TBI system, by precisely controlling the air/fuel mixture under all operating conditions, provides as near possible complete combustion.

In order to regulate the fuel delivery in such an efficient manner, then ECM receives electrical inputs from various sensors about engine operating conditions. An oxygen sensor in the main exhaust stream functions to provide feedback information to the ECM regarding oxygen content in the exhaust. The ECM uses this information from the oxygen sensor, and other sensors, in modifying fuel delivery to achieve, as near as possible, an ideal air/fuel ratio of 14.7:1. This air/fuel ratio allows the 3-way catalytic converter to be more efficient in the conversion process of reducing exhaust emissions while, at the same time, providing acceptable levels of driveability and fuel economy.

The TBI unit is made up on 2 major casting assemblies: (1) a throttle body with a valve to control airflow and (2) a fuel body assembly with an integral pressure regulator and fuel injector to supply the required fuel. A device to provide idle speed (IAC) and a device to provide information about throttle valve position (TPS) and included as part of the TBI unit.