p1518 is easy to do. Open up the IMRC box on the bulkhead and chemical metal the return spring in place so it shuts. Did mine a year ago and run loads better but now mine keeps giving that code even though the spring is still ok so sod knows. Theres a online step by step guide on doing it.
As for the o2 sensor Id put a new sensor in but theyre quite expensive and you need the front one