Wierd throttle issue

[Adammm]

First off, thank you in advance. I know the basics and then some about cars but I'm no mechanic and I do most of my own work in friends' garages.

I have a 1994 Nissan Altima with the KA24de engine. First off, I was trying to put on a cold air intake which I ended up remounting the stock air filter housing back on because it wouldn't work with the mass air flow sensor not on and my intake wouldn't fit on the sensor. I gave up and relised it wouldn't be worth it anyways since it is kind of a cold air intake with the tube running from behind the head light and under the car.

After that, we tried to take off my heat shield and ended up trying to cut it off because we couldn't get at the O2 sensor to take it off. We cut most of the heat shield off and my friend accidentally hit my O2 sensor and severed the wire a little bit. The heat shield is still on and we left it like that at this point.

Next he started messing with my throttle. Here I know nothing about this. He tightened a nut to make it idle higher. Well, it doesn't idle higher.

I'm not sure which one of these three things caused it but the next day I noticed when I'm taking off, it kind of lags and jerks. It still starts and runs fine for the most part but when I accellerate slowly it is jerky and the RPMs go from approx 1500 to 1900 back down to 1400 and then up to 2000.. and so on until I hit like 2500 where it's fine after that. After about 25mph it's fine. Or if it is warmed up its fine. Anything over halfway on my temp gauge it won't do it. Is it the O2 sensor, throttle, or something I did with the intake? Or would I need to have someone look at it?

Thanks so much,
Adam