My 1993 Nissan Maxima will not stay started When you put it in reverse it stalls I changed the fuel pump air filter fuel filter has new plugs its getting gas has no check engine light on?

Have you ever checked the air intake boot, that goes from your air filter, directly to your engine? It's a short, large ribbed hose that's rubber, but it's probably as hard as a tire now from age. Check between the ribbing on the hose to see if there's any holes or deterioration in the intake boot. Also, check to make sure that all the clamps on the boot (and all other hoses coming from the air filter, into the engine) are very tight and fully secure. If you do have any holes or deterioration in the air intake boot, then you can simply apply A LOT of auto Duct Tape around the entire boot (ribbed hose), until no air is able to escape or entire the boot. When I say A LOT of duct tape, I mean to duct tape the he!! out of it. If you don't want a duct-taped, yet functional air intake boot under your hood, then you can order a new one. I did this to a 1995 Nissan Maxima that had the same exact symptoms listed in your question & it works fine to this day.