1986 Toyota pickup - sudden idle problems

I was performing the 90K mile maintenance on my 1986 Toyota pickup, and
decided to run some Sea Foam through it just to be sure everything was
clean. I poured about 1/4 of the can slowly into the carburetor of the
warmed up (and running) engine. It then coughed, backfired through the
carburetor, blew out smoke and died. It restarted, but since then it
won't idle at all, but will stay running very roughly if I give it lots
of gas.

I read somewhere else that Sea Foam can screw up the sparkplugs. So I
took all of them out and cleaned and inspected them. No change. The
engine will start but then die immediately unless I give it a lot of
gas and keep my foot on the pedal. As soon as I let my foot off of the
pedal, the engine sputters and dies.

Did the Sea Foam cause this? I'm very disgusted, because the engine
was running fine beforehand. Next time I'll leave well enough alone.

Jason