I've added an after market exaust manifold , recently a new catalytic converter , and tps sensor.
latley when I drive my car will kinder sputter and when I drive some times the rpms will start to drop and try to catch ,
I have an air intake on it but the intake air temperature plug isn't plugged in. I haven't had it plugge in for maybe 5 months so it doesn't make sense for it to star acting up now , the check engine light codes are 12 and 24 . I do have an oil leak that I will be fixing in the next couple of days , is it possible the leak could be contributing to the problem ? If anyone can help please let me know . It is a 1995 st204 manual transmission

You really need the air temp sensor plugged in, it's one of the 3 sensors the ECM uses to calculate airflow into the engine.