Is it bad to only change 1 plug in a v6 the car has 90000 miles

do so, get a platinum tipped quality plug , it will fire threw oil fouling if that cylinder is bad . inspect the old one for clues

Depends on your budget? If it works just recall in a note when changing the others at the service interval that they should be ALL changed i.e. The spark plugs! I would definitely just replace that one coil/plug to save some $$$.

change them all. Otherwise make sure the one changed matches the other 5 as to type.

You never ever just change a spark plug , change all of them & in a 15 year old car might be a real good idea to install new wires ..

Ok lets backtrack on my statement! If Collegeboy has kept up on the maintenance on regular intervals and wires plugs coils were regularly inspected Then changing one spark plug same brand type as what comes out and the coil then I would be OK with changing one! Now if he is truly in college struggling to make ends meet! ( see my comment on budget) then I would check the system spark plugs, wire/coils ( some coils are integrated with the wires i would have to decide how much I can afford! College now costs 8 X more than in 1980 ! I was trying to empathize with Collegeboy if he was on a budget ! This was the basis for my comment! In other words, how much can this person afford? Got cash? Splurge! Got moths? Keep it running ? Patch one and do the rest when the $$$$ is there. Just trying to " keep it real" as the kids say!

Thanks for all the input. I have only had car 2 years , the wires have been replaced but I believe the plugs are original. The car is showing me a code of misfiring on cylinder 2 and the back 3 plugs look really hard to get to? This is my I wanted to see if I replace one plug will it mess things up?

College is you found this helpful hit my MARK HELPFUL LINK Thanks Papa If you can afford it get those plugs replaced ! if you know they have never been replaced! And replace the one coil! If this helps hit my button! Thanks