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I convinced my bud to get a ALH engined TDI but it's got a hunting idle. The car got a thorough checkover, new filters, and everything else looks good. But on cold starts, the idle sometimes goes up and down about 100 rpm. Once it's warm it smooths out. Any ideas?
2002 5 speed Golf if it helps.
 

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In addition to the basic steps above , if you have a VAG-COM, now called VCDS tool, check the all sensors to see what the ecu sees. Some areas to note are the MAF and fuel injection balance, quantity injection, coolant temp sensor.
 

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Maybe, you could try diesel purge and see what happens. It won't hurt anything. But the idea of using the vag com to check idle balance is that some cylinders need more fuel than others, it could be because the engine is worn on some cylinders or that there's a fueling issue. Try looking with a vag com tool.
 

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Maybe, you could try diesel purge and see what happens. It won't hurt anything. But the idea of using the vag com to check idle balance is that some cylinders need more fuel than others, it could be because the engine is worn on some cylinders or that there's a fueling issue. Try looking with a vag com tool.
Exactly, try free and basic checks first. But you really need a VCDS, they used to be called VAG COM, to do more detailed checks and look at the idle issue. It could be MAF, slowdown shudder, injector balance, or other mechanical issue. Maybe even a timing problem or faulty timing belt job.
 
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