why is my 2000 mazda mpv still acting crazy

it started howling so changed the iac fixed that but still popping or back fire in the air filter when accelerating changed master air, cleaned throttle body no difference. It idles at 7rpm to get it to go I have to give very little gas or floor it once moving sputs and sputters jerks even at freeway speeds still does the same. If I do not keep the rpms up at a light it barley moves so I pump the gas. It makes popping noise in filter and then goes but runs bad as explained. To accelerate and the most all of the time it has to kick down raising the rpm to 4-5 red lines at 6.5 must have running start to get up hills even a slight incline. do not want to blow it up....Please help!!