I Have A 98 Chevy Camaro 3.8 And I Have Problems Cause I Allways Have The Codes P1665 And P0300 I Replace The Evap Selenoid And Evap Canister And Fix All Vacuum Leaks And Stil The Problem Is There. Some Body Can Help Me Whith This?

I'll try...
They may be two seperate things or they may be related.
A.) P0300 = engine misfire detected. This code means that the computer is logging times when all the cylinders are not firing correctly all the time.
Cause(s) could be Bad - Plugs, Plug Wires, Coil(s) and other items in the firing circuit.
If you've recently changed plugs check to see non are cracked or bad. Check each plug wire for damage. Check Coil(s) for correct primary and secondary readings.
(note: A bad computer (ECM) can also cause this code - read through below...)
B.) P1665 = A defective Internal Driver in Computer (ECM) output to EVAC solenoid circuit. (note: this P1XXX is a specific manufacturers 'GM' code and not a universal trouble code like a P0XXX)
This can be caused by defective wiring in the circuit causing the problem - so check all the wiring from the computer to the solenoid to be sure they are in good shape and not open or shorted.
If the wiring and solenoid (you've already changed) check out okay then it is internal to the computer. You will need to replace computer (ECM) to repair.

Hopefully others with some experience with OBD-II will chime in if I've missed something.
Hope this helps;
John

thank you so much I'll try that