My 4cyl 2008 Accord EX has been in the shop for a week. It starts, but there is a strange metallic noise (not very loud but enough to notice) in the engine. When i try to drive, it struggles to pick up speed. I had the speed pedal all the way to the floor to get about 20mph - slowly. My mechanic inspected the car and thinks i need to replace the engine. Has anyone had similar issue?

 

There are way-WAY too many possibilities for what may be causing your issue or issues to diagnose over the internet. If you don't like the diagnosis given by your mechanic, I suggest you take it somewhere else for a second opinion.