My Yaris accelerate too slow !!! any suggestions ??

[tk-421]

A wider exhaust tube will affect your top end, simply because you're losing back-pressure. Heavier/wider wheels will also affect your overall speed because of added rolling resistance.

At this point the only thing that comes to mind is to check your air filter and all related couplings. The filter should be as clean as possible, and the couplings should be very tight to make sure that there aren't any leaks adding to the problem.

You might also want to consider getting rid of any dead weight (ie try to keep your trunk empty), which actually makes a substantial difference with our cars.

Hope that helps!