can anyone tell me why when I uplug my maf sensor my car runs good with no misfire, rough idling, or spitting rich fuel isses. But then when I plug it in although the codes go off, I get a rough idle, misfire, and rich fuel mixture. I am aware that when its unplugged it puts the car into "safe mode" where it shoots a even mixture of rich and lean, but what I dont understand is its a brand new maf sensor and why when its plugged in it screws up the whole car. Im trying to figure out what is causing the issues when its plugged in. Its an OBD1 1992 Lexus SC400

 

I had the same issue with my LS400 almost 20 years ago, maybe not as bad but it never ran right, and I never got it figured out, spend thousands trying to get it fixed. With such an old car, don't even bother trying. Get a new car.