Where in heaven's name is the ecm located on my 94 isuzu P'up? Online, no one (including Alldata/Auto zone)

First, it wouldn't idle without dying-now it won't even adjust to under about 1500 rpm! "Check Engine" comes on routinely, but It never sets a code, just the straight "1-2", meaning all systems go. Once I locate it, I know I can open it to at least look for outright heat damage, but beyond that, I've found NO info on diagnosing it. Naturally, it's OBD-1....Gawd, thanx in advance....