i keep getting a p0507 i have changed out everything what else could it be 1996 chevy cavalier 2.2l

Question

i have replaced these things and cleaned everything

top end gaskets
bottom end gaskets
iac valve
pcv filter/hose
spark plugs
air filter
crank postion sensor
evap purge solenoid valve
oil pressure switch
oil level switch
new radiaotor hose
new thermo stat
enigine coolant temp switch
cleaned throttle body when we exchanged all gaskets
deleted code and it keeps coming back