[Parky8]

start with basics- when was last tune up ie; spark plugs,fuel,air filters
then if they are good, recently replaced.
check exhaust for restriction- ie cat converter.
A muffler shop or decent shop should be able to test for back pressure.
I use to use a vacuum/pressure tester. drill a small hole in front of cat and use a metal tube to insert into drilled hole. pressure should not be over 2-3 psi. then check after cat . Then check timing belt- iff applicable

good luck