Would you mind if I "opened/open" the window

Question

Which one of the followings is correct?

Would you mind if I opened the window?

or

Would you mind if I open the window?

Ps: like 2 if condition
If I were you / If I was you (both is okay but usually used to "were")
so it is the same condition or not?

Answer 1

Would you mind if I opened the window?

This is the most grammatically correct usage. You should use this.

Would you mind if I open the window?

This, while technically incorrect, is still used a lot by native speakers.

Your other two sentences are in a similar situation:

If I were you

This is correct. While normally we use was in the singular case, for hypotheticals we use were.

If I was you

This, while technically wrong, is still used all the time by native speakers who don't understand the nuance of the subjunctive mood.

Answer 2

This is the 2nd would condition. Both conditions are unreal.

For example:

Would you accept that job, if they offered it to you ?

1. He has not accepted the job.
2. He has not been offered the job.

This is the same as

1. He does not feel annoyed at that moment.
2. The window has not been opened.

Would you mind if I opened the window

The above sentence is correct.

Answer 3

Would you mind opening the window? - it's a request Would you mind if
I open the window? - it's asking for permission

Would you mind not smoking? - it's asking sb to stop smoking, or not to start doing it when we see sb is going to do it.
Would you mind if I smoke? - it's asking for permission to smoke

Are these both acceptable and the same in meaning?    
    "Would you mind if I opened the window?"    
    "Would you mind if I open the window?"    
Both are quite acceptable. The meaning is identical.     
Some people believe the use of "opened" makes the request a little more polite