Jeep stalling problem

Hello everyone,
I have a 1996 Jeep Cherokee with a 4.0L engine. It has 205,000 miles on it. I recently had to replace my altenator. While losening the tension bolt for the serpentine belt I broke what looked to be a temperature sensor on the engine block. After I got the car back together the car would not start unless I constantly gave it gase. I went to the dealership and bought a new one and installed it. It seem to fix the problem. However, when I went out the next morning to start the car it would turn over but would not start until I actually gave it gas. The moment I take my foot off the gas the car dies. However, if I put the car and gear and am able to get the car into 3rd gear (it's an automatic, so I have to actually drive on the road with two feet) it runs perfectly fine and does not stall. It only happens on cold startup after the car has been sitting for an extended period of time. I have a feeling it is a computer problem but I am not sure. Any thoughts would be greatly appreciated. Thanks so much for your help!