Check for vacuum leaks all over the place, starting with the intake snorkel between AMM and throttle body. Check for vacuum leaks at the injectors and intake manifold using spray carb cleaner. Lower on the list of possibilities is the O2 sensor. Make sure wires to the throttle position switch and the idle air controller are in good shape; ditto for the temp sensor which talks to the ECU.

If you suspect the check valve to the brake booster, you'll get a significant change in idle speed - not just a little blip - when you step on the brakes while the engine is idling.
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Thank goodness we don't get all the government we pay for. -- Will Rogers