I should have mentioned, the loose stud is at the front of the PPF, not the diff. Is that one supposed to spin freely? How do I fix?

the trans part has the same metal plate on top also. Have you tried a non-nylon nut with some locktite?

Not yet. The stud is sooo loose I thought I should address it before trying to get another nut in there. If I try to remove the entire PPF for purposes of reinforcement, am I likely to find more loose studs throughout?

IMO, using Loctite is a very poor "bandaid" fix. Even if you can get the fastener tight, it may work loose again EVEN THOUGH THE NUT IS STILL TIGHT on the stud. And, with a spinning stud, getting it loose the next time will be a bigger problem due to the Loctite.

Agreed. Any idea where to start in order to cure the spinning stud issue..

I am assuming you would rather not pull everything apart to fix it by replacing or welding the stud in place. So:

Looks to me that there may be room for 2 nuts on the stud. So, this is what I would attempt to do:
1. Dremel a shallow screwdriver slot in the end of the stud
2. Put neverseeze on the stud and screw a nut on, tightening the nut while keeping the stud from spinning using the slot
3. Put a 2nd nut on and tighten the 2nd nut to the 1st, while using the slot to keep the stud from turning
4. Using 2 wrenches, tighten the 2 nuts against each other.

If 2 full nuts are too tall, use 1 or 2 jam nuts instead.

Of course, my one tool I cant seem to find (dremel). :(

Well, you could try it even w/o the slot. With the lubrication of the anti-sieze, and the higher friction of the stud against its mounting surface, it might work anyway. Try it. What do you have to lose?

What is stopping the stud from falling right out of the car? I wish I could see up there.

it probably has a head on it. If you can pull on it and it doesn't pull through, it won't fall out once it's tightened.

A stud with a head, eh? Sounds like a bolt.

It might be... but the fix is the same... :/

dudemaaanownsanrx7-Can you show us some pics? I have a spare PPF and would like to reinforce it

I don't have any pics sorry.

You mean like this? ;)
https://www.rx7club.com/attachment.p...1&d=1261112073
https://www.rx7club.com/attachment.p...1&d=1261112073
https://www.rx7club.com/attachment.p...1&d=1261112073

I'm also try to find my old pics from this thread I made 3 yrs ago.

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/check-out-my-reinforced-ppf-527280/

^nice! thanks for sharing need to get around to doing that. What material/gauge did you use.

1/8" steel! It was only installed for about 6 months up untill I blew the engine later that year. Now it's just collecting dust. LOL!

Turns out it is a bolt. Go figure. To secure it while tightening the PPF mounting nut was a PITA. The bolt has a 7/8" head (pretty large) and the space above the trans is very limited. I ended up using a 1/2" drive stubby ratchet with an integrated flex head ($10 Harbor Freight including 1/4" and 3/8" drive ratchets too) and a shallow socket 7/8" and reached up and over the trans from the passenger side to hold the bolt, while hitting the locking nut with an impact deep socket. Not sure if I got the full torque, but I am hoping the locking nut is good enough. Better than it was before, at least.