so ive been trying to get my 2m/70cm mobile setup working decent for weeks now and the swr is all over the place depending on where i park. got a diamond nr770hb on the roof of my accord and sometimes its great, sometimes its terrible. checked all the connections twice and the coax looks fine. is this normal or am i missing something obvious? the radio is an ft8900r if that matters

ground plane issues for sure. your car body isnt big enough for proper ground plane on 2 meters especially if youre mounting near the center. try moving the antenna towards the rear of the roof or adding some radials. also check that mount - make sure its got good electrical contact with the body, not just sitting on paint

i had similar problems with my civic and that same antenna. ended up switching to a lip mount on the trunk and it made a huge difference. the roof mount looked cleaner but never worked right. also what kind of mount are you using? some of the cheaper mag mounts dont have great connection