I have an 1986 l98 auto. Car starts fine and idles at 800 -1000 rpm but after 4 or 5 minutes it jumps up to 1100 -1300 rpm and if I give it more time it goes as high as 1400 -1500 rpm. NOTE: this is with the car sitting still in my driveway

Once I put the car in gear it drives around town nicely at about 1000-1200 rpm. I feather the gas petal to a most of 1500 or 1600. When the car is under strain going up a hill or pressing the gas petal firmly for example, after 3 or 4 minutes the car will suddenly sputter and drop down a couple hundred rpm. It will then run rough at 500 - 800 rpm and I can feel a significant power loss. Considering when the sudden drop in rpm happens, and the fact that the lights dim for a second when it does, my friend told me it miht be electrical related. When I first got the car a couple months ago the problem wasn't that bad and I thought it just needed a tune. But now I think it may be another problem. Someone also mentioned dirty injectors could be the issue or the mass air flow sensor or Iac? Something about a loop the engine goes into

External factors: Gas gauge reads incorrectly but I just assumed it was a stuck float and would get around to it next weekend. Car has a bbk 52mm throttle body (dont know if its port matched), and the cats were removed right after the manifolds by the previous owner.

Im new to working on cars and have limited knowledge about the electronics, if someone who knows about tpi tuning and the electronics could help me out that would be great and if you need more information lmk thanks