Hello everyone I am new here. I recently bought a 99 blazer zr2. It runs great for the most part but when I leave it sit for a while (an hour or more) it has a lot of hesitation when I start to go. Even if I let it warm up for a good ten minutes. The weird thing about it is it will back fire and sputter if I give it gas. If I let off the gas and let the rpms go back down it will "kick in"and is usually fine and runs great until I leave it sit again. Is this a common thing that happens after time Its got nearly 140000 miles on it. My dad owned it before me and it did it to him on rare occasions but not as often since I got it. He replaced the fuel filter ran good gas and changed the vaccum lines as well. Thanks for any help truly appreciated!

 

Has it had a recent tune up? Plugs, wires, cap, rotor, pcv, fuel filter, air filter??? I had this happen from failing o2 sensors and a cat before too.