2000 Saturn SL1 IDLE SPEED

I AM WORKING ON A 2000 SATURN WITH A 1.9 L 4 CYL SINGLE OH CAM THE ENGINE WILL START FINE , BUT RUNS AT ABOUT 2500 RPM FOR ABOUT 30 SEC TO 1 MIN THEN WILL SLOW TO ABOUT 1200 TO 1500 RPM IN NEUTRAL ANS ABOUT 1000 RPM IN DRIVE. IT RECENTLY HAD THE TIMING CHAIN REPLACED AND THE TEMP SENSOR WAS LATER REPLACED ALONG WITH THE PLUGS AND WIRES. IT WAS RUNNING FINE UNTIL IT STARTED REFUSING TO START WHEN WARMED UP BUT AFTER SITTING SEVERAL HOURS IT WOULD START AND RUN FINE
THANKS FOR YOUR HELP