Your vehicle is shaky while idling or at low speedsIf your truck suddenly feels unstable while idling, it might be a sign it's time to change the filter. The reason it could feel this way is the filter isn't letting enough fuel get through, which means it could be filthy and clogged as a result. The same thing applies to instability at low speeds, like leaving your home or accelerating from a stop sign or stoplight. Another sign your filter could be clogged is your vehicle running fine once it gets going to higher speeds.Uneven fuel distribution is a telltale sign that something's wrong, so if you're experiencing any of these symptoms while driving your diesel truck, the fuel filter could need a swap. Of course, it's difficult to tell if that's the reason your truck is idling weirdly, but it's a very common reason why that's the case. If you're within the recommended window to change out your filter, it's best to take a look.