1999 Chevy Lumina idles rough

1999 Chevy Lumina mileage: 110,000. When starting engine, car cold (overnight for example regardless of outside temp 20-60 degrees) the engine wants to rev up to 3000+ rpm and idle back down to 2-300 rpm or just quit altogether. Unless you sit there and hold the rpm steady at about 2200 rpm, it will not idle at the correct rpm of 7-800 rpm. Car has done this since we have had it at 85000 miles. Took to Chevy dealer last winter (cold temps mean you can’t start car and go in where it is warm and wait for it to warm up!) And they could not find anything wrong. Replaced a hose and that is all. Nothing electronic found to be bad. Hope you can help with this problem. It would be greatly appreciated! Thought that you may have seen this problem on this engine (3.4L) and have a fix for it. Thanks