I'm considering trying a thru rail fuel injection cleaning to try and improve my off throttle stumble (which despite my best efforts is not completely eliminated). Amazon sells them for about $50 but they do not come with cleaning fluid, nor do they specify what to use.

This is what I'm considering. https://a.co/d/j482uly

Probably a high concentration of something like BG44k, mixed with gasoline?

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2003 X5 3.0i MT, White, 161k