Except Calif.

Turn engine off. Label and disconnect all vacuum hoses from EGR vacuum modulator. See COMPONENT LOCATIONS  under INTRODUCTION. Replace EGR vacuum modulator if it does not operate as follows:

• Block ports "P" and "R" with finger. See Figure. Blow through port "Q". Air flows freely out of filter.
• Start and run engine at 2500 RPM. See CONNECTING TACHOMETER  under INTRODUCTION. Block ports "P" and "R" with finger. Blow through port "Q". There is strong resistance to airflow out of filter.