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A Sluggish Bug
Eric Seifert, Automotive Technical Editor

A customer recently noticed that his 2002 VW ® Beetle ® turbo diesel had lost its pep. After he scheduled an appointment, I went to work researching the symptom he described.

Perform repair steps 1 through 9; if any of these steps reveals a problem, repair or adjust as necessary and perform a road test prior to continuing on to step 10. All steps should be documented using VAS® 5051/5052 (or equivalent) printouts (if related to warranty claim).

A Hand Vacuum Pump may be required to diagnose the problem.

Applicable Vehicles:
98-03 New Beetle ® with1.9L TDI (ALH)
99-03 Golf ® and Jetta ® with 1.9L TDI (ALH)
01-03 Jetta Wagon ® with 1.9L TDI (ALH)

Repair Procedure:
Review safety procedures in ALLDATA® before beginning.

  1. VW Diesel Figure OneECM ground connection.
    Inspect ECM ground (GND) connection for corrosion, poor or no connection.
  2. Injection pump timing.
    Check start of injection pump timing.
    Tip: An adjustment to the upper range is advised.
  3. Snow screen (if applicable) at intake air duct.
    Check snow screen, located below left front fender in air duct (3), and clean as necessary
    Inspect air cleaner element (1) for proper installation.
    If air cleaner element is deformed due to improper installation, this may cause the MAF sensor to fail.
    Replace air cleaner element as necessary.
    Tip: Always check with VW or your local supplier for latest part revisions.
  4. W Diesel Figure TwoVacuum hoses.
    Check integrity of all vacuum hoses and connections, and repair as needed.
  5. EGR valve and intake manifold air flap (integrated in EGR valve).
    Remove intake hose (1) at EGR valve
    Remove vacuum hose from EGR valve (2).
    Connect hand vacuum pump to EGR valve (2).
    Apply vacuum and make sure that air flap (arrow) opens and closes freely.

    If flap does not open and close freely:
    Replace EGR valve / flap.
    Tip: Always check with VW or your local supplier for latest part revisions.
  6. W Diesel Figure ThreeMAF sensor and EGR valve including solenoid valve.
    Check correct function of MAF sensor and EGR valve including solenoid valve.
    Tip: Since both systems work closely together, if one system malfunctions it will directly affect the function of the other. Therefore it is important to follow the procedure carefully.
    In addition, the MAF sensor must be full-load tested.
    If MAF sensor readings are out of tolerance (even if no MIL ON condition or DTC is present), before replacing MAF sensor or EGR solenoid valve:
    Ensure wiring is OK and electrical connections are clean and functioning properly.

    If wiring is OK and electrical connectors are clean and functioning property:
    Replace MAF sensor
    Tip: Always check with VW or your local supplier for latest part revisions.
    If MAF sensor failed full-loaded test, and after replacement of MAF sensor full-load value still cannot be attained:
    Check turbocharger
  7. Crankcase Ventilation System.
    Inspect and verify that it is functioning to OEM specifications.
  8. Engine oil level.
    Check and adjust to proper level if necessary. DO NOT OVERFILL!!!
  9. Fuel Quality.
    If condition occurs suddenly, fuel quality may be inferior

    If fuel is suspected to be of poor quality:
    Drain and refill fuel with known good quality fuel.
  10. Check for Carbon build-up.

If all previous items are functioning according to specifications and the vehicle still exhibits poor throttle response, it may be necessary to physically inspect the EGR valve and intake manifold as (in higher mileage vehicles) there may be excessive carbon build-up in the intake manifold and/or EGR valve.

Tip: While some carbon build-up is normal and not a concern, excessive carbon build-up is related to fuel quality and soft driving behavior (operation at low speeds and short driving distances), under extremely cold and damp operating conditions.

To inspect for carbon build-up:
Remove EGR valve and inspect and record depth of carbon in the valve and intake manifold.

Normally carbon build-up is not a concern; a problem may occur only if it is excessive (greater then 10 mm). If the carbon layer in the EGR valve and/or intake valve is greater then 10 mm (50% - 60% clogged):
Replace EGR valve and/or intake manifold.

If the EGR cooler is clogged more then 50% - 60% in its flow area:
Replace EGR cooler.
Tip: Always check with VW or your local supplier for latest part revisions.

If new parts are not available, or if it is more economical, the intake manifold and EGR cooler can be cleaned.
Tip: Prior to cleaning, the intake manifold and EGR cooler must be removed from the engine to ensure that no carbon particles enter the engine.

Written by ALLDATA Technical Editor, Eric Seifert. Eric is an ASE certified Master Technician and Engine Machinist. He is a graduate of the De Anza College Automotive Technology Program, with 20 years of independent shop and parts store experience.

©ALLDATA LLC. All rights reserved. All technical information, images and specifications are from ALLDATA Repair. ALLDATA is a registered trademark and ALLDATA Repair is a mark of ALLDATA LLC. All other marks are the property of their respective holders.

New Beetle, Golf, Jetta, Jetta Wagon, VAS, VW and Volkswagen are registered trademark names and model designations of. All trademark names and model designations are being used solely for reference and application purposes.

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