Hello! I have a 2008 automatic Pontiac Vibe with around 130,000 miles with a decent amount of engine vibration at lower rpms. I notice a lot of engine vibration when the idle is under 1000 rpms after it has warmed up. 1000+rpms feels very smooth. I know inline 4's are known to vibrate, but I'm not sure how much is too much. I cleaned the MAF and throttle body, replaced the spark plugs, flushed the transmission fluid, tried some fuel additives, and changed out the front and rear engine mounts with new OEM ones. The only thing that made a difference was changing the motor mounts with the car feeling more smooth (the rear one had a split rubber), but the lower idles still shake the cabin a lot and the engine is visibly shaky when looking under the hood. Is this something I should worry about? No codes or anything. 

PS in case this is relevant-- max mpg I've been able to get is 24mpg, which seems low seeing how I am soft footed on gas and brakes. Transmission is also occasionally a little jolty going between lower gears (less so after transmission flush), and coming from driving stick all my life, I feel like it stays in first gear too long before deciding to switch to 2nd. Other than that, the car drives great!