What are symptoms of a bad spider injector

I have a 2000 astro. 120k recent plugs cap wires. Had meineke figure out a alternator problem awhile back and they mentioned I will eventually need a new spider injector because my van was occasionally tripping the engine light and would run rough. Last time I checked to code it was a misfire. This weekend the van ran pretty bad intermitanly. Runs and stumbles like it's going to stall..like a vacuum leak but then clears up. Used to only happen if the van was running then shut off and run again in short amount of time. I dont use the van much so I didnt care but now its worse. I did a spider valve a few years back on a 94 astro I used to have with success but I forgot the symptoms. Just want to make sure before I go pulling the intake. Any advice appreciated