Hi,
The L9110 is a much more upto date device and works well, these modules are available very cheap on ebay, etc. THe L9110s chip works a bit different to some others, in that the 2 control input pins are DIR and PWM, so with only 2 pins you can control direction and speed the L283/298 needs 3 or 4 control lines, depending how you do it.
Have you tried changing the battery packs over as I suggested?? it really will make a difference to your motor speed. What tutorials have you seen, NOT Instructables! their full of rubbish and errors....
Does the motor look like it's well made and capable of a good speed, it's likely to be about 6V, what was the power pack in the car? when you got it?
Regards
Mel.