- Checking the Basics

Before performing any diagnostic procedures on the Throttle Body Fuel Injection System, pertaining to engine performance, fuel economy or exhaust emission complaints, perform all normal diagnosis which would apply to a vehicle not equipped with this system.
When diagnosing the system, always begin with the ``Diagnostic Circuit Check'' which will verify proper operation of the system. When performing the ``Diagnostic Circuit Check'', the drive wheels must be blocked. On some engines, the oxygen sensor will cool off after only a short period of operation at idle, which will put the system into open loop operation. To restore closed loop, run the engine at part throttle for several minutes and accelerate from idle to part throttle a few times.