2001 IS300 lost of power

[rhwindley1954]

My 2001 IS300 has a lack of power.  At times it takes off normal. Other times it takes off very slow as if it has no power.  I have changed the timing belt and spark plugs yet the problem still exist. No check engine light. Not sure what to do next. Can anyone help? Thank you.

[TrevC]

You could look at the exhaust being blocked...see how much gas comes out when revved and if it sort of whistles then there could be a blockage