93' 88 Royale Timing

Hello, i have a problem with my oldsmobile and am not too car savvy so i was hoping someone could help me out.

About 4 days ago my a/c started working again after about 6 months of not working, and it was a hot day, so i left it on. After about 20 minutes of driving, i came to a stop and when i put my foot on the gas to take off, it didnt quite have any hp to it.

It did take off but took about 15 seconds to get to 30 mph. I also noticed that the car was vibrating way more than usual. So i turned off the a/c to listen more closely and it stopped. I then turned it back on, and the vibrating started up once more. I then decided to just turn it off (a/c wasnt worth me getting stranded) and the same thing started happening with the a/c OFF now.

Its now been 4 days and my car simply has NO oomph to it. I cant even get on the darn interstate, its really that bad.

If anyone could please shed some light or maybe just give me some suggestions it would be greatly appreciated.

may i also mention that it is backfiring a little when i put the gas all the way down.

Also, can where is the timing mark on this car located? I called my local Autozone, but they were of no help, as usual. :/
Thanks for your time.

ok, i found out the problem is the tps. the trouble code said tps adjusment, so does that mean i should tweak it or buy a new one? How hard is it to install a new one?