Pics will be posted below. Have them on my phone and am typing this on my computer.
So to start off, I bought a 1994 DX sedan a couple of years ago and eventually discovered somebody had swapped the d15 for a d16y7. Don't know details of the swap, but I scrubbed off the front of the block and head when I was confused as to why the d15 parts just wouldn't fit like they should. Moving on. The car has been getting terrible mpg, something around 24 highway. Its a manual car (manual trans, windows, mirrors, locks, everything). Upon doing more digging I discovered that the vac line to/from the fuel pressure regulator was different from others I've seen. It had a T in it running across the car to some part that is unknown to me. My dad has a 1997 LX with the same motor, but does not have this box and I haven't seen anything like it in any pictures I've seen of any d15 cars. As stated, there is a vac line going to it. There is also wiring from the firewall to this part and a hard line from the part to the firewall. I unhooked it and taped off the T to keep from having a vac leak and the car seems to run fine. No problems going from heat to AC; nothing seems like it isn't working because of unhooking the vac line and I really just want to figure out what it is. Thanks for any help!

 

 

Will wait

 

Thanks, just waiting on pics to be approved currently

 

My guess is aftermarket cruise control. Does the wire through the firewall lead to the foot pedals?

 

Not that I know of but I really can’t tell. Car doesn’t have anything on it to indicate cruise control. I can’t find any kind of part number or manufacturer on it

 

aftermarket cc i'm assuming as well

 

Cruise control seems to be the consensus, so I’m not as worried about having the vac line unhooked now. Thanks for the input, I’ll check later to confirm where that hard line goes.

 

The actuator cable in your final picture above enters the firewall where the OE cruise control cable would be located... and likely connects to the top of the throttle pedal inside the cockpit. This definitely suggests an aftermarket cruise control system.