A 2004 Jetta PD with 101k miles experienced intermittent stalling at idle and low speeds. The timing belt and fuel filter were recently replaced. Initially, a failing lift pump was suspected and replaced, reducing idle shake but not resolving the stalling. The engine restarts immediately after stalling and misfires noticeably during the 10% of occurrences when the problem manifests. Applying throttle above 1500 RPM temporarily overcomes the issue.
Further diagnostics using VCDS (measuring block 013) revealed the following idle stabilization values:
- Cylinder 1: -1.51
- Cylinder 2: 0.68
- Cylinder 3: -0.07
- Cylinder 4: 0.89
Cylinder 1 consistently displays negative values, sometimes dropping as low as -2.0. Cylinder 3 fluctuates and becomes positive during driving. While all values fall within the specified range of -2.8 to 2.8, the consistently negative reading for Cylinder 1 raises concerns about a potential injector issue. Further investigation into the ALH timing using VCDS and consulting forums like tdiclub.com is recommended to determine if timing is contributing to the stalling problem. Common topics on these forums related to ALH engines and VCDS diagnostics often cover timing belt installation, injection pump timing, and troubleshooting stalling issues.
Although the idle stabilization values are within spec, the persistent negative reading on Cylinder 1 suggests further diagnostics are needed. The next steps could involve checking the injector wiring harness for damage, performing a compression test, and logging injection quantity deviation values using VCDS. The forums on tdiclub.com offer a valuable resource for troubleshooting ALH engine problems and interpreting VCDS data. Users frequently share their experiences and solutions related to similar stalling issues, providing insights into potential causes and fixes. Properly diagnosing and addressing the root cause will ensure reliable engine performance and prevent further complications.
