Adjusting Idle


Test requirements:

Engine must be in perfect mechanical condition and ignition timing set correctly.

1. Run engine to operating temperature (about 80° C/176°F).

2. Remove air cleaner.

5. Connect CO tester and separate tachometer according to manufacturer's instructions. Separate 2-pole plug connector when connecting tachometer. Use jumper wires to bridge connectors and provide terminal for connecting black/violet wire to tachometer or engine tester. Black/violet wire normally goes to terminal 1 of the distributor. The tachometer or engine tester is connected to this wire, which normally goes to terminal 1 of the distributor.

3. Detach air hose at air pump and plug open end of hose.

4. Check if manual accelerator lever is at bottom stop.

25-8 Adjusting Idle

I, 1976 - Printed in Germany

Porsche 930 Tachmeter

6. Turn air correction screw on throttle valve housing until specified speed is reached. Use special tool P 229 c.

Remove plug with seal in top of mixture control unit.

8. Guide adjusting wrench P 377 in.

Turning clockwise richens mixture; counterclockwise leans mixture.

Caution a) Always adjust CO from lean to rich. Example: if idle screw setting is too rich, first turn counterclockwise further than necessary and then clockwise to nominal setting.

b) Never apply pressure to adjusting wrench while adjusting (engine stops).

c) Turn control screw very slightly as very small turns alter amount of CO in exhaust gases considerably. Maximum adjustment on mixture control screw is 1/2 turn.

d) When checking (or adjusting) CO, plug adjusting hole before taking CO reading. If hole ist not plugged, extra air will be pulled into control unit giving wrong reading.

9, Remove wrench. Caution

Never leave wrench in adjusting hole when accelerating engine as this could severely damage mixture control unit.

10. Accelerate engine briefly.

11. Wait until CO tester shows a concentration of exhaust gas at idle speed. See Page 25 - 15 for adjusting data. If necessary repeat procedure.

12. Install air cleaner again and recheck idle speed and CO content.


Complete adjustments as quickly as possible to prevent overheating intake ports.

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