I'm not sure exactly what the problem with your car is but you could look at a couple of things:
1) Make sure that the car is set up the same on both sides (left and right) - make sure the upper arms are the same length, make sure they attach to the same points on the chassis and rear hubs. Make sure that the roll center points (where the lower wishbones/arms attach to the chassis) are of the same type from left to right and that they're the right way round. If you have rear hubs with vertical ball studs (pointing up rather than forwards/backwards) then make sure each side has the same amount of spacers (if any). Do the same for the front.
2) Take the shocks off the car. Put the car on 10mm blocks (or something you know the height of) and measure the droop, make sure that the droop is the same from left to right. Make sure that the amount of thread protruding from the wishbones onto the chassis is the same from left to right, if it's not then the wishbone is bent or moulded out of shape in some way (or the attachment of the hub to the wishbones may be screwed up or something). Make sure that the wishbones roate freely, look at the rotating bits (hinge pins, attahment to chassis, attachment to hubs/steering arms) and make sure that nothing is tight there.
3) Look at the shocks, measure them and make sure that they're the same length. Make sure that they both rebound (the outwards movement of the shock) to the same point and measure again.
Make especially sure that the car is built exactly the same (and correctly) on both sides, I've bought a few cars second-hand and had to totally rebuild them due to them being mangled by the last owner. Worst example was an Mini M05 (Tamiya) most of which wasn't actually Tamiya parts.
Spent as much returning it to stock Tamiya state as I would have buying a new M05. Oh well!