Low Rev at Idle and other little problems.

Car Specs:

Gold III GL 4 door '93. 117000 Km on it.

It's been about a week that when the engine is cold (Im in Canada at -10 temperatures) I heat the car up for about 10-15 minutes before leaving for work.

I noticed that when I stop at a stop sign, the engine almost stalls. If I turn on the heating the engine goes down to a very low rev then gradually comes back up to par. If I turn on the Back window Defrost it does the same thing.

Since This morning, I noticed that when I stop, the same problems occur but the Oil light blinks and then stops. Even when the engine is hot it still does the same thing now. I am not quite sure what the problem is.

I was thinking that it might be the Alternator (Original part), Or Perhaps the Battery, but I rather ask experts. All the belts where changed on the Car, I got my Oil changed 5000 Km ago.

Any help would be appriciated.