OK, so my pizza delivery car, 1990 Civic 4wd (D16A6) is having some issues lately. After getting my stuttering problem fixed (plug wires) it has developed an issue with idling. It starts out around 1500rpm, then it will drop down to around 4-500 practically dying, then jump back to 1500. It will go as high as 2000 and drop back down. The car is also running rich.

I've been told by a few different people they think its probably my O2 sensor. I just wanted to consult the peanut gallery before I dropped $45 on a sensor and get all dirty. Let me know guys, appreciate it.