engine running up and down on cold starts

It sounds like you have a large vacuum leak, yes. So you need to find it. Check all the hoses, maybe you left a hose off or loose when you removed the throttle body. Is the engine holding coolant? Is there a sensor connector left loose? When I last did a t-stat on this engine, I had to be sure to re-connect all the sensor connectors, did you do the same? Any Check Engine Light on? If so , get the code, that will really help.