'95 Civic LX - engine shakes at startup, shuts off when put in reverse

[choltrop]

A few weeks ago my car broke down all of a sudden on the highway cause I blew the radiator. Replaced the radiator no problem, car was working again, three days later the engine started shaking on startup. Thought, this is weird, didn't notice any problems after running the car for half and hour, turning off, and then turning over, so thought nothing of it. Now when I start the car after having let it sit for any amount of time, a minute to 12 hours, the engine block is jumping up and down under the hood (saw while starting with hood up) and the exhaust pipe is shaking. No idea what the heck is going on, anyone have a clue? Do I need to tighten some bolts on the exhaust pipe or something?

 

[Wreckless Hype]

Welcome to the Club.

You let the car idle for 12 hours?

Any CEL? Smoke? If you give it gas, does it smooth out? Did you flush the system properly and bleed any air out?

 

[choltrop]

No CEL showing, air was bled out when replacing the radiator, and when it starts up shaky giving it gas is a 50/50 stops the engine/smooths it out. Normally I wait 2-4 minutes for the shaking to stop, then I'm able to shift out of park/use the gas without it shutting off the engine. Earlier comment about leaving it from 1 minute to 12 hours was with the car off, not idling.