Overhead problem lead to laggish (Jumping)

I have Overhead spike issue in my game and when I run my racing game in iPod Touch 4th gen and it's lag (jumping), but it's smooth on my iPad3.

When I keep turning off my active gameObjects, I still unable to find what's wrong in my scripts. I do researches and found that bad programming practices and bad programming behaviors could lead to this problem. I keep disabling my gameObjects, until everything is gone, and found out the Overhead problem is still exist even all my gameObjects are being deleted!?

How do I solve my problem? It's just a simple racing game. This is not good because FIFA 13 can be play on the iPod Touch 4th gen but my simple tiny game couldn't??

Draw calls - around 50, 1.4k tris and 7.8k verts....

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