This works w/all the non-EGR EJ22's (most manual cars from '95-98, and any '90-94 EJ22) and should work on the non-EGR JDM EJ25's, too, and doesn't require drilling/tapping the driver's-side cylinder head. (You'll need to get a single-port exhaust header/y-pipe for the '96-'98 EJ22.)
EGR = Exhaust Gas Recirculation valve
Edit: Also, the EJ18 from the Impreza should work. (Thanks to Matt167 for the reminder.) But be aware that it gives up 50Hp/Torque to the EJ25.
This modification eliminates the EGR pipe that originally attaches to the EGR valve on the IM and the driver's side cylinder head.
See pic (from EJ25, but same idea on EJ22):
This REQUIRES an EGR-equipped intake manifold ('95-98), but changing the intake manifold (IM) isn't that tough, esp. w/the engine out (remember - the EJ22 SOHC and '96-'99 DOHC use different IM's- not interchangeable!). I don't know of anyone that's successfully bypassed the EGR valve by using a resistor or any other electrical modification.
I've put over 2K miles on this and not had an issue. NO CEL/Check Engine Light. Car's MPG is still the same.
Overview of what I did: I ran a hose from the EGR valve and T'd into the IAC hose so the EGR valve sees flow...it doesn't care where it's from apparently.
For the EGR valve connection, I found 2 fittings @ the ACE hardware store that fit together. I believe it's 3/4 that screws into the EGR valve on the IM, then a 1/4 barbed fitting. Put some thread tape on to seal it...it screwed in tight w/out any issues:
I then ran short piece of PCV hose into a 90° elbow. PCV hose is same ID as the breather hose on the valve covers.
Here's the EGR-side installed:
From the elbow I ran another piece of PCV hose to a reducer fitting w/a short piece of PCV hose from the T-fitting in the IAC hose, as the IAC hose has a larger ID than the PCV hose I used.
So far, I've not had a CEL and car runs the same as before. (Don't tap into the breather hoses as you'll have blue smoke out the tailpipe! )
EDIT: I did this same mod on my '96 Legacy (bought 8/2015) when I used the EJ22T heads (no EGR port), and on 10/25/16 I got a P0400 EGR code. I cleared it and it came back next time I drove the car. I replaced the BPT - back pressure transducer - that sits on top of the EGR valve and has 4 vacuum lines connected - 3 on top; 1 underneath. No codes after a week's worth of driving. I used a TOYOTA part that I PullandSaved months/years ago. I guessed this was the issue, and it takes about a minute to swap it out.
Thanks again for the input from everyone on here and to member 987687 for the idea.
Edited by wtdash, 04 November 2016 - 03:49 PM.