1999 Cadillac fuel system

Recently bought a 1999 Cadillac Seville STS, With only 42,000 miles. I’m pretty sure it set for a few years then was drove with the same gas. It struggles when I try to crank it how ever it eventually starts every time. It does puff a little black smoke right at start up and the rpms are rough for about 30 seconds while it sputters and shakes. but nothing after that. And it runs perfect after the rpms level out. I have replaced fuel filter, spark plugs, air filter, fuel injectors and still is doing it. There is no check engine light. So idk what to try next. Thanks if anything

You left something out of your description… have you filled the tank since you bought it? Since you changed all those parts? How many tankfuls? Have you tried some injector cleaner in the fuel tank?

Yeah I’ve ran 3 or 4 tanks already with injector cleaner

I’ve only ran injector cleaner on the 1st and the current one

The more clean fuel you run through the better the car will get. I’d continue with the injector cleaner, too.

Try cleaning the mass air flow sensor and the throttle body as well.