A Toyota dealer or Toyota specialty repair shop could isolate
the problem down to:

1) Carbon clogged EGR Valve and pipes
2) Bad EGR Valve vacuum modulator
3) Bad EGR gas temperature sensor or some other
part of the EGR system depending on the year of
your Camry, 4 cyl or V6, Calif or Federal Emissions

Non-Toyota specialty auto repair shops don't even own
a Toyota factory repair manual let alone have
much Toyota specific experience so that's why
they give out Gomer Pyle advice like: " we could try replacing
the air filter and gas cap to see if the check engine light
goes away."

Paul Cherubini