1978 Saab 99 BaseFACTORY OEM SERVICE PROCEDURE

Deceleration Valve: Testing

NOTE: To avoid faulty reading caused by radiator fan cutting in while performing test, disconnect thermal switch wires while test is being performed.
  1. With engine at normal operating temperature, disconnect hose between carburetor and deceleration valve and check for vacuum passing through valve. If vacuum is present, the adjusting screw on the deceleration valve has to be screwed in further until the valve is closed. Reconnect hose between carburetor and deceleration valve.
  2. Connect a tachometer and adjust idle speed to 900 RPM. Open throttle to obtain 3000 RPM. Release throttle and measure time required for engine speed to drop from 3000 RPM to idle. If deceleration valve is correctly adjusted, time should be between 7-8 seconds. If not, valve must be adjusted.
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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