Volkswagen Golf/Jetta 2 manual

Cold acceleration enrichment system - testing
Fuel and exhaust systems - K-Jetronic fuel injection - 8 valve engines / Cold acceleration enrichment system - testing


1 When the engine is cold (below 35°C), acceleration is improved by briefly enriching the fuel mixture for a period of approximately 0.4 seconds. This cold acceleration enrichment will only operate if the thermotime switch, the diaphragm pressure switch and the throttle valve switch are shut off.

2 To check the system, first check that the cold start valve is operational.

3 Detach the wiring connector from the cold start valve and connect up a test lamp to its terminals.

4 Detach the wiring connector from the thermotime switch and connect a length of wire between an earth point and the connector No.2 terminal W (green/white wire).

Do not earth terminal G (red/black wire).

5 Run the engine and allow it to idle, at which point the test lamp should not light up. When the engine is quickly accelerated, the test lamp should light up briefly (0.4 seconds) (see illustration).

12.5 Cold acceleration enrichment system check
12.5 Cold acceleration enrichment system check

Cold start valve connector earth contact (2) (green/white wire to W terminal)
Do not earth contact 1

6 If a fault is evident, check the wiring connections, the throttle valve switch and the diaphragm pressure switch.

7 The diaphragm pressure switch can be checked using an ohmmeter. Detach the wiring connector from the end of the diaphragm pressure switch, then start the engine and allow it to idle. Using the ohmmeter, check the resistance reading between the contacts. An infinity reading should be given.

8 Accelerate the engine briefly and check that the resistance drops briefly and then returns to infinity (see illustration).

12.8 Diaphragm pressure switch test
12.8 Diaphragm pressure switch test

1 Diaphragm pressure switch 2 Vacuum connection for switch (yellow) 3 Vacuum connection for spark control

9 To check the throttle valve switch, detach the switch lead connector and measure the resistance between the switch contacts. An infinity reading should be given.

10 Now slowly open the throttle valve to the point where the switch is heard to operate with a click. The ohmmeter should give a 0 ohm reading and the clearance between the throttle lever and the idle stop must be between 0.2 to 0.6 mm (see illustration).

12.10 Throttle valve switch check
12.10 Throttle valve switch check

1 Throttle valve switch a = 0.2 to 0.6 mm

11 If necessary, adjust the switch by loosening the switch (underside of throttle housing) and positioning a feeler blade of 0.4 mm thickness between the lever and stop. Move the switch towards the lever until the switch is heard to operate, then retighten the switch and check adjustment.

12 If the throttle valve switch is being removed, prise the connector bracket apart to release the connector.


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