um best not to mess with the idle srcew(i've done it my self, bad things happened)
did you happen to get the code?
manual or auto trans?
ever replaced the ECT?
do this: go out and buy a can of sensor-safe carb and choke cleaner, spray it into the throttle body, the carbon build-up not leting the throttle plate close can act like a vacuum leak. next, spray the carb cleaner around the intake manifold gasket with the engine running. the later SOHC like to suck the gasket in, if the engine bogs down, there is your problem. the next step would to be remove the EGR and clean it out to, but i would rather have the code before doing any more.