A 2004 Jetta PD with 101,000 miles recently started experiencing intermittent stalling issues. The timing belt and fuel filter were recently replaced. The engine stalls about 10% of the time when slowing to a stop, idling, or driving at low speeds. It restarts immediately without hesitation and the problem occurs regardless of engine temperature.
A failing lift pump was suspected and replaced, resulting in reduced shaking at idle but the stalling persisted. During stalling episodes, misfiring is audible and applying throttle to 1500 RPM allows the engine to recover.
Further diagnostics focused on idle stabilization values using VCDS (measuring block 013). The readings obtained were:
- Cylinder 1: -1.51
- Cylinder 2: 0.68
- Cylinder 3: -0.07
- Cylinder 4: 0.89
These values fluctuate, but Cylinder 1 and Cylinder 3 consistently show negative values at idle. Cylinder 3 becomes positive when driving. Cylinder 1 never reads positive and occasionally drops to -2.0. While all values fall within the specified range of -2.8 to 2.8, the consistently negative readings for Cylinder 1 raise concerns about a potential injector issue.
Further investigation is needed to determine if the Cylinder 1 injector is faulty. Possible next steps include:
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Injector Quantity Adjustment: Check and adjust the injector quantity adjustment values using VCDS. Significant deviations from the ideal range may indicate a problematic injector.
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Injector Swap Test: Swap the suspected faulty injector with a known good one from another cylinder. If the negative idle stabilization value follows the injector to the new cylinder, it confirms a faulty injector. If the problem remains on Cylinder 1, the issue lies elsewhere.
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Compression Test: Perform a compression test to rule out mechanical problems with Cylinder 1, such as low compression.
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Leakage Test (Return Flow Test): This test measures the amount of fuel returned by each injector. Excessive return flow from Cylinder 1 would further indicate a faulty injector.
By systematically investigating these possibilities, the root cause of the intermittent stalling can be identified and resolved. Addressing the negative idle stabilization value on Cylinder 1 is crucial to restoring reliable engine performance.
