1990 Other Chevrolet Models Chev 454 idles high and blows bl

I have a chev 454 with TDI in a motorhome. It started missing and sputtering and seemed to be flooding out, blowing black smoke. I removed the catalytic converter and put a straight pipe in its place thinking it might be stopped up. I put Lucas engine treatment through it. I did a tune up, dist cap, rotor, plugs and wires, the replaced the 2 fuel injectors, the iac, fuel filters. Now when I start it cold it idles high and the idle fluxuates from 24-3500 rpm, vacuum at the intake manifold is 20" and fairly steady. It puts off a little blue smoke. Then when I let it warm up and shut it down and restart, I have to put the accelarator to the floor to start it and it sputters and blows black smoke and won't stay running. I let it set overnight and it starts good again with the same high idle, a little missing. Every other start has the same result. I still have the catalytic converter out and plan to replace it with a new one when I get the engine running right. Thanks so much for your help, this is driving me crazy.