Car problem my engine bobs?

I have a 2001 honda civic and my engine bobs when it's on park I'm not sure if it's I mixed 87 gas & 91 gas but I want to know what's the sources that cause the engine to bog. Thank you please help don't want to take it to the shop

Most likely its your motor mounts. To check motor mounts and to determine exactly which ones need to be replaced:
set your parking brake. With the engine running have an assistant apply the brake. With one foot on the brake and one foot on the accelerator put the transmission in reverse. Work the throttle so that engine torque is applied. If your front mounts are bad in need of replacement you will see the engine lift up. Next put the transmission in drive. Again one foot on the brake the other on the accelerator. Work the throttle to deliver engine torque. This will tell you in what condition your rear mounts are in. If the engine lifts up (and you will see exactly what i'm talking about if they are bad) then replace broken mounts. If no movement is seen in either reverses or drive than your problem is someplace else. But if its "bobbing up and down" then 99% sure its your mounts.
NOTE: most cars have 3- engine mounts 1- transmission mount if its front wheel drive. If its rear drive 2- engine mounts 1-transmission mount. Some have more.