You did not state what kind, or year, or engine size of your vehicle never the less the first answer given is on the right tract. You may have up to four O2 sensors so you may have to have a diagnostic check on it. Further, and in conjunction with the O2 sensor(s) you my also need a tps (throttle position sensor). good luck

Cars run rich mostly because the O2 sensors are old or defective. Not sure about that idle problem. This and the idle problem are jobs for a trusted mechanic unless you’re good with cars. Or adventurous )