P0506 – RPM Lower Than Expected (VW)
When the powertrain control module (PCM) detects an engine idle speed below the pre-programmed RPM limit, the P0506 code is set.
The PCM uses a series of “tables” to determine the proper engine rotations per minute at a given throttle (accelerator pedal) position and engine load. When P0506 is tripped, it indicates that another problem is very likely…it’s very rare for a P0506 code to be triggered alone. There are usually other codes.
For this reason, P0506 is considered a diagnostic trouble code (DTC) rather than a trouble code (TC). Most commonly, a P0506 will be accompanied by a P017# or similar oxygen sensor or MAF sensor code.
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To diagnose a P0506 DTC, begin with the other codes also tripped. These other codes are more likely to lead to a solution. If the P0506 is tripped alone or the other codes showing are not powertrain related, then the problem is almost always going to be a vacuum leak or air restriction in the intake. Occasionally, a faulty PCV (positive crankcase ventilation) valve could be at fault, but this usually trips related codes. It is also possible that the PCM itself is bad and triggering random codes as a result (again, this is unlikely).
Fixes for a P0506 will vary. Vacuum checks should be a first priority, as well as a complete check of the air intake system, including filter changes and a look at the MAF (mass air flow sensor) and PCV. The EGR valve may also need cleaning. Quite often, the code is a one-time trip and can be cleared to never return.
Author Jason Lancaster never has engine idle problems, because he’s always got his foot on the gas pedal. When he isn’t racing around, he’s talking about engine trouble codes for VWPartsVortex.com, a website that offers OEM Volkswagen parts at wholesale prices.