1996 Jeep Cherokee Jeep only starts if gas is pressed while

I am having an issue in that my Jeep will not start unless I press the gas while turning the key. It also will often not idle and would not stay running if I let go of the gas, while other times it will stay idle after starting up and pressing the gas and drives just fine. I brought it to a local mechanic who saw the same issues and seemed to think it may be a problem with the CPU, but I wanted to see what some other options to check into, as the mechanic was unable to find a used CPU to use and this could be a costly repair. Thanks in advance!