98 cherokee won't stay running

stock 6 cyl. in mornings it will start up ok. put it in gear after warm-up and it will take off. when i ease up on gas at slow speed it dies out. does this several times. when i am on the main road and up to speed it runs fine for the rest of the day.morning temps from 12 to 35 farenheit.today it wouldn't idle at all. had to keep foot on accellerator at about 1800 rpm's to keep it running.again after i got it to speed it ran fine. someone told me about a solenoid on top of the engine at the firewall.does this control idle? any ideas? thanks. art