What does the vapor canister do? Is there harm done in unplugging the sensor for it under the hood? We have an 89' cutlass that ran for a good year with the vapor canister sensor diconected from the canister.

 

The EVAP canister captures the evaporative emissions from your gas tank, and recycles them back into the intake so they can be burned.

I would definately not unplug the solenoid. It's possible that the valve might fail open, and then you'd have an intake leak that would manifest in poor performance. Many people have struggled with poor performance only to find that it was the EVAP canister purge valve solenoid. Why would you want to do that to yourself?