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Daveyboy20

530d intermittent rough running

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Hi guys, I have a high mileage 530d with FSH and it drives very well indeed. However, the idle feels missy - particularly when it's cold. If I slowly raise the revs in neutral it seems to miss most at around 2k. As soon as I drive its not noticeable and doesn't 'seem' to even do it at 2k. Anyone have any suggestions?
 
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Most likely injectors have seen better days. If you have access to INPA (BMW diagnostic software), have a look at injector correction values. Acceptable tolerances are from -4 to+5, usually ones with high positive value are bad. High negative values usually are just to compensate those with positive. From my own experience, you can try to run through system liqui moly diesel purge, I'm usually quite skeptical about all kind of additives and cleaners, but that stuff does wonders. Bought my e39 two years ago, after a month idle started to jump up and down, one injector was around+6, so well over. I disconnected fuel lines from tank, extended them a bit to get in bottle filled with diesel purge, and just run 1 litre of clean diesel purge through system. Two years later (45k miles) that injector still have correction values around 0. About month ago another injector (not the same as previously) started to show values close to+5, this time I waited for fuel tank to be on reserve, poured 1l of liqui moly stuff into tank and drove until it's nearly empty. And again idle is perfectly smooth with injector correction values dropped closer to 0. Of course it doesn't guarantee to work always, most likely it helps if injector nozzle is dirty and party blocked, but I would say it's worth a try before replacing injector.

 

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