With Volkswagen Tester VAG 1551

Air/fuel mixture is always controlled by the Motronic control unit. The purpose of the idle mixture adjustment is to fine-tune the mechanical adjustment of the metering unit and match it to the electronic controls. When properly adjusted, the differential pressure regulator is operating near the middle of its range, controlled by the oxygen sensor and the control unit. The idle mixture screw does not affect the actual air/fuel mixture.

Idle checks or adjustments will be valid only after the CIS-E Motronic fault memory is clear. Any faults stored in memory must be corrected, and ignition timing also must be correct. Service technicians use special electronic test equipment to access the control unit fault memory and display coded information. For more information refer to TESTING AND INSPECTION.

Making these checks and adjustments together is very important to both driveablity and emissions control. If the equipment necessary to accurately perform this work is not available, we suggest turning the job over to a local repair shop that has the needed test equipment. In a properly equipped shop, these checks and adjustments can be made quickly, accurately, and at resonable cost.

NOTE: The first step in any Motronic system troubleshooting must be to check the control unit fault memory, it is important to find and correct any faults that may be indicated before continuing with testing procedures. For more information refer to TESTING AND INSPECTION

TEST AND ADJUSTMENT CONDITIONS

1. Engine oil temperature must be at least 176° F (80° C) and radiator cooling fan has operated at least once.
2. All electrical consumers switched OFF (radiator cooling fan must not be running during checking or adjusting).
3. A/C switched OFF.
4. Idle switch is functioning properly. For more information refer to TESTING AND INSPECTION.
5. Fault memory must be clear of stored faults. If any are found, they must be corrected and then fault memory erased before proceeding. For more information refer to TESTING AND INSPECTION.
6. The exhaust system must be free of leaks.
7. There must be no engine vacuum leaks.
8. The oxygen sensor must be connected and operating properly. For more information refer to TESTING AND INSPECTION.
9. No fuel pressure measuring equipment connected.
10. If injector lines were loosened or replaced, run the engine up to 3000 rpm several times and then allow to idle for at least 2 minutes before performing any adjustments.
11. Throttle cable adjustment must be OK.

TEST AND ADJUSTMENT SET-UP

1. Put vehicle in PARK or NEUTRAL set parking brake.
2. Turn ignition switch OFF.

Checking Motronic Ignition:

3. Connect VAG 1367 engine tester using VAG 1367/8 inductive pickup, or a suitable strobe timing light and tachometer may be used.

CO Tester Hookup:

4. Remove the cap from the CO tap tube that comes from the exhaust manifold and connect an EPA approved CO tester to the CO tap tube using VW special tool #6006-0019 high temperature silicone connecting hose, (or equivalent).

NOTE: Non-approved connecting hoses may dramatically alter your readings. Adaptor must be connected tightly to CO tap tube to prevent measuring errors.

5. Remove tamper proof plug from air flow sensor assembly.

Crankcase Housing Breather Hoses:

6. Disconnect crankcase housing breather hoses #1 and #2 from breather housing #3 and place hoses such that only fresh air can be drawn in. Calibrated insert #4 must remain in hose #2.
7. Ensure that ignition switch is turned OFF.
8. Disconnect harness connector from differential pressure regulator.

NOTE: Access to the differential pressure regulator is limited. Trace the wiring harness from the differential pressure regulator up to the harness connector located on the right shock tower, connector is positioned in a small holder. Use this connector for test equipment hook-up instead of the connector at the differential pressure regulator.

Checking Differential Pressure Regulator:

9. Connect test adaptor VAG 1315A/1 (or equivalent) between differential pressure regulator and harness connector.
10. Switch suitable multimeter such as the Fluke 83 multimeter to 200 mA range.
11. Connect multimeter to test adaptor VAG 1315A/1 using jumper wires from VW 1594 adaptor kit.
12. Turn ignition switch ON.
13. Control current must be displayed as positive polarity (90 to 110 mA). If negative polarity is displayed, reverse multimeter test leads.
14. Turn ignition switch OFF.

Diagnostic Connector Hookup:

15. Connect VAG 1551 with adapter cable VAG 1551/1 as follows.
a. Black wire to black diagnostic connector #1.
b. White wire to white diagnostic connector #2.
c. Blue wire not used.

TEST AND ADJUSTMENT PROCEDURE

1. START engine and let idle.
2. Press 1 button to select "rapid data transfer" mode.
3. Press 0 and 1 buttons to select engine electronics.
4. Press Q button to enter input.
5. Press right arrow button.
6. Press 0 and 4 buttons to select "initiate basic adjustment" function.

Initiate Basic Adjustment XX Display:

7. Press Q button to enter input, display will appear as shown.

Initiate Basic Adjustment 00 Display:

8. Press 0 button twice to display group 00, display will appear as shown.

System In Basic Adjustment Display:

9. Press Q button to enter input, display will appear as shown.

NOTE: The display channel values are in decimal form.
2000 is the maximum number of rpm's that can be displayed at this setting.
When this function is selected, the DIS (digital idle stabilizer) is switched OFF and the carbon canister solenoid valve is CLOSED.

10. Observe channel 9 of display.
11. Display value must be 5.
12. If value other than 5 is displayed, check that A/C is switched OFF and idle switch is OK. For more information refer to TESTING AND INSPECTION.

IGNITION TIMING

1. Check ignition timing, checking value is:

4° to 8° BTDC

2. Adjust ignition timing if needed.
3. Loosen distributor and rotate until specification is correct, adjusting value is:

6° ± 1° BTDC

4. Tighten distributor bolts to specification.

IDLE SPEED

Idle Air Bypass Screw 16v:

1. Check the idle air bypass screw, it should be in the seated or bottomed position, it is not used for idle adjustment.
2. Idle speed rpm's can not be adjusted.

CO CONTENT

1. Check CO content before adjusting and record the value.
2. To accurately check CO content idle must be:

800 to 1000 rpm

CO Adjustment Motronic:

3. Adjust differential pressure regulator control current using a long 3mm hex wrench in CO adjusting screw, adjusting value is:

2.5 ± 2.5 mA (must fluctuate)

4. If control current does not fluctuate, check oxygen sensor and oxygen sensor control. Refer to TESTING AND INSPECTION.

CAUTION: During CO adjustment:
Do not push down on wrench while adjusting.
Do not accelerate engine while wrench is inserted in CO adjusting screw.
Remove wrench after each adjustment and briefly raise engine speed before reading control current on multimeter.

5. Observe CO content. CO volume must be:

0.2% to 1.2%

6. Turn ignition switch OFF.
7. Remove test equipment.
8. Reinstall any hoses that were disconnected during testing, reinstall cap on the CO tap tube.
9. Install new tamper proof plug for CO adjustment screw in air flow sensor housing.