I don't know what happened to my other post, but I still haven't figured out where this goes. The car seems to run allright, but I want to make sure to cover all bases. It comes out of the loom for both O2 sensors on my 1990 CRX HF w/B16A swap.

 

im almost positive its the plug for your stock EGR valve.

 

yea egr the hf crx was designed to get really good gas milage so it had an egr unlike the rest of the ef's