easy, get an exra stock computer, need not work, and use its connector as the plug in for you megasquirt. mount the MS unit right next to the stock computer, and just switch plugs. as a bonus, if one of you computers should happen to fry, you swap plugs and keep driving.

AIR is air injected into exhaust to improve cat efficiency and warmup time, as well as providing the cat extra O2 on throttle closing. may not be used on 88...usualy 100% computer controled on newer cars.

EGR is Exhaust recirculated into the intake at part throttle to keep down combustion temperatures, reducing ping and NoX. often disconected by people who dont know what they are doing and think it reduces power. Usualy 50/50 computer & Mechanical control. should actiate above a certain speed once engine is warm with throttle not full open or full closed.

this is just a general outline, I am not super hip on Volvo emission systems as mine is diesel and has none. I am, however trained as a smog tech.