1991 Other Isuzu Models bad idle on start

My isuzu has a 2.6L engine. I can start it when it hasnt beed driven for 4 hours without problems. But when I start it within that time it will start and baraly run. It idles extremaly bad shaking the whole truck. But after you drive it for 5 minuts it clears up and runs good. Until you turn it off and start it again. I have changed the temp sensor, mas sensor, fuel injectors, idle solonoid. Ecm module, and checked the fuel presure, changed spark plugs, checked timing, and still wont run better. And all the gaskets are good(intake manifold, throttle body, i-tec)please help me. Thanks