Well, the reason for not getting a proper range for your car remote is the antenna of your remote. There are couple of do it yourself techniques which can prove helpful.
1. Apply thin sheet of tin foil. You may need to open the remote and create a little tinfoil sheet on the opposite side of the LED.
2. Another method involves opening the remote and locating the antenna. The antenna should look like a silver box. Scape out a little silver and solder a small wire to it.
3. There is an old technique which says holding the remote to your chin and pressing the remote button makes it work better. Though there is any scientific proof to explain it, a large number of users have admitted that it works! Could be a myth, but what's wrong in trying it out?
Please note that the first two methods need you to open the remote. If you have no sound technical knowledge, do not open it, it may damage your remote.
Live....and Let Live!