chulisohombre
1/2 ton status
if you had a auto thre would be a vaccuum line for the modulator on the tranny.that could have been what that was for.fixing a vacuum leak would definitely make it run better.it would be lean and you would have to gas it more to get the rpms up.on idle you would also have to open the idle screws more to dump more fuel to compensate for the xtra air in the system.so it would run rich when you try to fix the idle and not run right off idle to the higher rpms.i bet you can now turn in the idle screws some and get it to run cleaner now.good find.and good luck on the retest.
