Hello. I have a 2003 Frand Cherokee Laredo, 6 cylinder. I have replaced the cylinder head, intake manifold, timing chain, water pump, thermostat, serpentine belt, thermostat, spark plugs, spark plug rail, and all hoses. I went for first start tonight and cherokee started up and idle was 4000 rpm. I could not reduce the idle speed as the throttle was positioned at the idle speed. I could only raise the rpm and not reduce it. Does anyone have any thoughts on what the issue is and how to fix it?