Trouble code 31 canister purge circuit

I have a 96,5.2,4wd,120k.
Last night my Cel came on, I did the key trick this morning and it came up with code 31 and the truck wouldn't stay running. It started up as long as I had my foot on the gas but when I let off it died. I started to check vac and I have about 25in at the solenoid and about 6in coming out(even when the truck is cold. I took the valve apart and cleaned it there was some charcoal residue but no damage to the internal parts. The haynes manual says I shouldn't have any vacuum there when the truck is cold, if I do it's the valve is bad. But prior to the test it says to start the truck and let it idle which I really can't do, but those are my results when I keep my foot on the gas. I tried to check the voltage but I am doing this alone so I couldn't start the truck and check the voltage at the same time but with the key on I had 6v. So I am at a point now where I am trying to understand how this works. Haynes says it isn't suposed to be on when the vehicle is cold. I plugged the line going to the canister(trying to simulate no vac) and it wouldn't start.
Am I chasing the wrong problem and maybe this code just popped up for fun. The valve is $55 and it will take a couple days to get so I don't want to make the wrong call. Also the fuel pump was replace about 8months ago the truck turnsover strong and I have good vac. Any ideas or opinions are greatly appreciated.

Thanks for you help.
Alan

I would contact your nearest dealer and find out if your truck has any outstanding recalls . Certain 1994 to 1996 trucks had a recall to replace the purge canister and the purge solenoid (free of charge) .

Thanks for your help. I actually figured it out on Tuesday and I haven't had time to post an update. The code as far as I can see is unrelated to the starting issue. If anything the purge cansiter code was due to a loose(dry rotted,cracked end of the line coming from the purge canister or the cleaning of the purge valve. The starting issue was caused by the IAC. I was able to remove it and the vehicle started fine and just reved high. I manually depressed the plunger and re installed it and it idled high again until I pressed the gas a few times it lowered but was still about 1500rpms. I noticed that the plunger was fully extended when I removed it so I think it was just choking out the engine. Replaced the IAC with a new one and it works fine.