Cold start high idle when outside temp below 50°F

Hi y'all! I have a 94 with 99 engine in it. I've been chasing the high idle when it cold outside problem on it for a while. When the ambient temp above 50-55°F it cold start idle around 1k5 rpm for 2-5 mins and drop back to 900rpm. But when it below 50°F it idle at 1k9-2k rpm for like 15-20 mins and then drop back to 900rpm and running fine after that. I've checked no vacuum leak, new throttle body. Does anyone have the same issue or what should I do to fix it ? Thank you all !