4Funner8301

Hi everyone, I am new here but hope someone here can help me with a problem. Recently I bought a 91 4runner, it runs great and has a lot of power still left in it. I recently cleaned some grounds, and when I put everything back together I ran into some issues. I am pulling Code 31 Air Flow Meter Signal or Vacumn Switch Signal. I am getting crap for gas mileage, and it has a really hard time starting in the morning. I know I need to replace the oxygen sensor, but what should I be looking at doing with my other problems. Is there anything I should be cleaning or inspecting, eventually I would like to get rid of the air system, and put an aftermarket one on there. Also when I drive down the road its really sluggish, then something weird happens, the car jerks as the engine light goes off, then she runs like a champ, then everything comes back on and its back to running like . Please can anyone point me in the right direction.