Could be bad IACV gasket, or dirty sticking IACV. What does your vacuum data show when you are coasting in gear?
Around here it's $40 to get a smoke tester hooked up to check for leaks. I built my own, but after using it once, I will never sit there with a spray bottle of soapy water, brake clean, etc. ever again. So worth it to find all your leaks in 10 minutes.