Hi, im new so this is my first post. hopefully itll be a very helpful one...
So, i have a 1992 Sc300 5 speed.
car has an hks exhaust, intake piping w/ bfi mod
other than that the motor is stock

NOTE: this only happens when warm, and it doesnt happen all the time throughout the rpms. it may start when accelerating from a dig but goes away around 3.5-4k. but other times it is continuous throughout the band.

so heres what is happening/happened
I got the car with a bum *** clutch so two days after i got it i replaced it at a local shop
once that was done i figured i would do the usual tuneup (plugs, vc gasket, oil change)
well, after finishing the plug and vc install i threw some seafoam in the tank and started it up hoping it would help clean things out after i just did the tuneup.
car ran fine for a good 15 mins, get in it to go drive and dont make it 1/2 mile down the road and it starts to misfire. so, i replace the plugs with the old ones thinking thats the issue (didnt gap them right maybe...) car did the same thing...ran good for 15, drove 1.5 miles and misfires. so i said "**** IT" and drove the ***** home with the misfire only to find out its also leaking oil out of the vc gasket cause i missed tightening down a bolt on the cover. so, i get that tightened but it still misfires.

Flashback...
i had an issue with the fuel pump ecu and had to do the bypass to get it to run and drive(still had bad clutch)
the day before(day i got it) i had an issue of it backfiring when decelerating(under load) and it threw a cel. went to get it checked and when i fired up my car it was gone..odd. but i didnt care cause it still drove fine.

flash to present day of story....
car throws another cel, check it and its the o2. so im thinkin "DANG maybe that has been my issue all along, maybe the seafoam killed it and it was causing the miss"
fixed that and this time after 20 mins of running the misfire was back.
so, my question is this...
does ANYONE know ANYTHING that could help me. ive been told SO many diff things and thats why i used so much detail to better help someone maybe pinpoint it.

 

You want to run seafoam and then change the plugs afterwards, otherwise you run the risk of fouling the new sparkplugs with the seafoam and any crud the seafoam loosened.

Also when you did the plugs, did you do spark plug wires as well? If neither of those are the issue, take off your distributor cap and inspect the rotor and inside of the distributor cap for evidence of burning. If they look old, burned, or like the contacts are worn then consider replacing those. But I'd be willing to bet that you fouled the plugs when you ran the seafoam.