Code-12 on a 89 prelude Q's

[78civic]

Good evening, I've had problems with this prelude showing a 12 code and have cleaned, replaced several EGR sensors and that usually fixed the problem.
Well, I've done that 3 times now and I thought it was over but a good friend was over to see about purchasing it and the dang 12 code showing a cel!!

What else could it be? A bad vacume line in the big black box?
Any others know where else to look?
How much vacume should it pull for the light to go off?
This is the 3rd one..

I'm getting worried that it's going to scare away potential buyers.

Any helpful replies will be great!

E

 

[78civic]

AAAAaaaaaaaahhhh....! I get in it this morning, starts fine, NO CODE/blinky, Ran it for almost a half hour and still no code..

Maybe It just doesn't want to get sold.

If I get some time, I'll take apart the box and look for a leaking hose or other damage.

E