The O2 sensor. This is a common problem. I had it my dc5r. Nothing to worry about really (Cos i drove around for 2 weeks without a single problem).

Try cleaning and ensuring the wires/plugs are in properly 1st.

1st I cleaned with Carby/Brake cleaner. It worked well but not well enough.

2nd I took a blow torch, and cooked her a little, after cool down some wet sanding and hit her again wit brake cleaner

SUCCESS!