In the test one of the questions is Je ________ si j'avais une voiture.

Question

The answer to the question is Je partirais si j'avais une voiture.
However, my question is about "j'avais une voiture."  Why is it j'avais (imparfait) and not j'ai une voiture, considering that its in the present?  Is this related to the subjunctif? Cause I have a feeling this has to do with the subjunctif :D

Answer

HI Gio,
even though the subjunctive rears its head in many unsuspected places, he is not to blame for this one.
The example you quote is a "si"-sentence introducing a possibility. It dictates the use of very specific times and modi: the conditional in the main clause and the imperfect in the si-clause.
Je partirais si j'avais une voiture. -- I would leave if I had a car.
You see the same kind of construction in the English translation: a conditional (would leave) in the main clause and the imperfect (had) in the main clause. The use of the imperfect has nothing to do with the action being set in the past. It is used here -- in conjunction with the conditional -- to express a possibility.
-- Chris (not a native speaker).