egr

Acording to service manual 88 chev G-10 uses negative valve i notice
today mine is positive. Pumped vacuum to it and didn't hold any
1. Is it bad?
2. Does it make a difference neg or pos?

you cannot interchange positive and negative egr valves. i don't believe they are supposed to hold vacuum. a quick check is to flex the diaphragm with your fingers while the engine is running. if it stalls or almost stalls, the egr is working properly. if it doesn't change at all, the egr is faulty.

The easiest way to check it is to do a suck test. Get a clean section of vacuum line and connect it to the valve. If you can suck on the line and open the valve, it should be ok. If you keep getting air, it is bad.
I use a little suction pump to operate the valve at idle, w/no change in idle, the valve is bad. A good valve should always hold vacuum. One more tip, give the 1708???? number to a GM parts dude and get a Delco replacement. I have seen some cheesey replacement valves cause a lot of headaches (for a few do-it-yourselfers).
Good luck,
---TEX---

do both tests,