Hey guys. First post so apologies if it's in the wrong spot.
I've had this issue since replacing my front o2 sensor (04 WRX) if I have the sensor connected I get really violent surging when holding a constant speed and very jittery acceleration but no CEL. Without the sensor it seems to run fine but I have a light because it can't see the sensor (obviously) Any input would be greatly appreciated.

Where did you get the sensor from? If it's one of the cheap ones from eBay that could likely be your problem.
Your car will run better when it is unplugged as it is forced to run in open loop mode (where it follows the fuel map and makes no adjustments). Whereas when you have the sensor plugged in it tries to adjust the fuel trim for better fuel efficiency but with the cheap sensor sending inaccurate readings it results in poor drive ability.

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Limiter bash gets the gash

That would more than likely be the problem then Haha �� just wish I could get rid of the CEL.
Thanks for the reply ��