Terminal gives :command not found, when typing too fast
Your problem is actually not Terminal.app specific.

The problem is more caused by you being slow on the keys than fast actually. When you type the | (pipe) character you need to hold down the Alt-key. When you're typing fast, you're actually too slow in releasing the Alt-key.

This means that you're not actually typing a space before the next command. You're pressing Alt-Space which gives you a "non-breaking space" - which is not the same as a space, but it looks that way in the Terminal.

The "non-breaking" space is not seen by your shell as a command delimiter, but instead a part of a command or file name. And therefore you get the error that no such file or directory exists.

To solve the problem - just remember to lift your finger from the alt key before typing space.

Alternatively you can change your keyboard mapping so that Alt-Space produces an ordinary space. You can find a guide to doing that here:

https://superuser.com/questions/78245/how-to-disable-the-option-space-key-combination-for-non-breaking-spaces