Why does your impreza run lumpy after new plugs?

If your Subaru Impreza runs lumpy after installing new spark plugs, it could be due to a few reasons. First, the new plugs may not be properly gapped, leading to inconsistent firing. Additionally, if the ignition coils or wires are worn, they may not be delivering adequate spark to the new plugs. Lastly, there may be an underlying issue such as a vacuum leak or fuel delivery problem that has become more noticeable after the maintenance.