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2.3L Engine

  1. Ensure engine is at normal operating temperature. Ensure all electrical accessories and cooling fan are off. Turn ignition off. Remove cap from exhaust probe receptacle and connect CO meter. Ensure fit is snug to prevent exhaust leaks.
  2. On 100 & 200 models, remove vent hose from elbow at intake air boot. Leave elbow unplugged to draw fresh air through opening. Remove crankcase breather hose and plug cylinder head openings. See Figure . Crankcase vapors must vent to atmosphere.
  3. On 80 & 90 models, remove sealing cap from top of charcoal canister. See Figure . Remove crankcase housing breather hose and vent to atmosphere. Crankcase vapors must vent to atmosphere.
  4. On all models, connect Multimeter (US 1119) with Test Adapter (VW 1315A/1) to differential pressure regulator. See Figure . Set scale to 200 milliamps (mA) DC. Start and warm engine to normal operating temperature.
    NOTE: If injection lines were disconnected or replaced, increase engine speed to 3000 RPM several times then allow to idle for at least 2 minutes to bleed injectors and lines.
  5. Insert fuse in fuel pump relay. Malfunction indicator light must come on to indicate that ignition is stabilized for testing. Connect timing light and check ignition timing. Refer to the 5-CYLINDER IGNITION TIMING  table for timing specifications.
  6. If timing is incorrect, loosen distributor clamp bolt and turn distributor. Remove fuse from fuel pump relay. Increase engine speed above 2500 RPM then allow it to return to idle. Ensure Ignition timing fluctuates between 7-20 degrees. Tighten distributor clamp bolt.
    NOTE: Some vehicles are equipped with a malfunction indicator light that comes on whenever an emission related fault occurs. Fuse from fuel pump relay must be removed and engine speed increased above 2500 RPM to cancel fault display.
  7. Check idle speed. Idle RPM must be within specification. See the 5-CYLINDER IDLE SPEED & CO LEVEL SPECIFICATIONS  table. If idle speed is not within specification, check air intake system for leaks. Idle speed is electronically controlled and is NOT adjustable.
  8. If necessary, check differential pressure regulator current with oxygen sensor connected. Reading must fluctuate between MINUS 4 mA to PLUS 6 mA and CO level must be .3 - 1.2 percent.
    NOTE: On 80 & 90 models equipped with, turn A/C system on. If idle speed drops severely, check idle stabilization system.
  9. Disconnect oxygen sensor harness and check CO content. Reading must be .3-3.0 percent by volume. If CO content is outside range, adjust idle mixture. Turn ignition off. Remove rubber boot from mixture control unit.
  10. Punch hole in center of CO adjusting screw plug and drill a 3/32" hole to a depth of 5/32". DO NOT  drill completely through as adjustment screw will be damaged. Install a 1/8" sheet metal screw and remove plug using pliers.
    NOTE: DO NOT  push down on adjustment screw and DO NOT  accelerate engine with adjusting wrench in place. Remove wrench after each adjustment and accelerate engine briefly before measuring CO.
  11. Install rubber boot on mixture control unit. Start and run engine at idle. Using Adjustment Wrench (P 377), turn adjustment screw clockwise or counterclockwise to adjust CO reading. See Figure . Install new plug in mixture control unit.
5-CYLINDER IDLE SPEED & CO LEVEL SPECIFICATIONS

Application Idle RPM CO Level %
2.2L (1) 750-850 .3-1.2
2.3L (Except 100 & 100 Quattro) (2)
Checking Value 720-860 .3-3.0
Adjusting Value 720-860 .6-1.0
(1) Idle speed for automatic transmission is 670-770 RPM.
(2) Idle speed for 100 & 100 Quattro must be 670-770 RPM.
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