Volkswagen Workshop Service and Repair Manuals

Notes:

When checking the idling adjustment always check/adjust

• ◆ Ignition timing
• ◆ Idling speed
• ◆ "CO content" via duty cycle of the frequency valve

At the same time

• ◆ During the check/adjustment the Lambda probe remains connected.

Checking and adjustment conditions

• ● Engine oil temperature 80 °C.
• ● Electrical consumers switched off (the radiator fen must not run during the check/adjustment).

• ● Air conditioner switched off.
• ● Pressure gauge not connected.
• ● If injection pipes have been disconnected or renewed, the engine must be revved up to 3000 rpm several times and then allowed to idle for at least 2 minutes.
• ● Exhaust system must be free of leaks.
• ● Lambda regulation OK, checking =>page 25-99 .
• ● Ignition timing OK, checking =>page 28-41 .

Checking and if necessary adjustment idling speed and duty cycle (CO content).

• ‒ With ignition switched off connect engine speed tester (e.g. V.A.G 1367).

• If necessary use an aux. terminal for connecting to terminal 1 of the coil.

• ‒ Connected CO tester (e.g. V.A.G 1363A) with adapter V.A.G 1363/3 to CO measuring pipe.

Note:

The adapter must fit tightly on the CO measuring pipe to prevent exhaust gas leaks.

• ‒ → Clamp off hose -1- from idling speed boost valve.
• ‒ Pull off crankcase breather hose and route so that only fresh air can be draw in.

• Hose -2- from intake manifold
• Hose -3- from air cleaner

▸07.86:

• ‒ Disconnect hose -4- (from activated charcoal filter to intake elbow) from connector -5-.

08.86 ▸

• ‒ → Reposition angled connector -1- so that the free connection with restrictor is in the intake elbow. If no restrictor is fitted, pull hose of angled connector.
• ‒ Run engine at idling speed.

• ‒ → Check idling speed, necessary adjust on the adjustment screw -B-.
       Specification: 900 ± 100 rpm

• ‒ → To check the duty cycle connect tester V.A.G 1367 to connector -1- (wire blue/white) and pres "[nvlt ] %" button. Only use measuring cable V.A.G 1376/5 when the connector -1- has round sleeves.

Note:

On the Scirocco the connector -1- is located near the ignition coil on the wiring loom.

• ‒ Check duty cycle for frequency valve and CO content:

• Test readings:
• ‒ Duty cycle 20...70%, display fluctuates
• ‒ CO content 0.3...1.2 Vol.%

Note:

If the CO content is more than 1.2 Vol.% with a duty cycle of 20...70%, this is not due to an incorrect CO setting.

Possible causes:

• ● Fault in ignition system.
• ● Exhaust system leaking.
• ● Injector inserts leaking, loose.
• ● Fuel distributor defective (unequal injection rate at idling)

• ‒ If the cycle is less than 20% or more than 70%, adjust duty cycle to the setting figure with the CO adjustment screw as follows.
• ‒ Drill a 2.5 mm hole in the plug over the CO adjustment screw.
• ‒ Screw a 3 mm self tapping screw into the plug.
• ‒ Pull plug out with pliers.

• ‒ → Adjust duty cycle with CO adjusting key -A-.

• Specified setting: 50 ± 8%, display fluctuates

• ‒ Adjust idling speed if necessary.

Note:

When idling adjustment has been completed the crankcase breather hoses must be connected again. If the duty cycles and CO content the change, this is nit due to the setting being incorrect but to enrichment from the crankcase resulting from oil dilution caused by frequent stop/start operation. A long fast run will reduce the amount of fuel in the oil and duty cycle/CO content will return to normal again. At short notice this can be done by changing the oil.