1988 s10 blazer 2.8L. in park the idle is aroun 1500 rpm when in drive with foot on brake about 1200 rpm as seen on the dashboard tach. is this normal ? can it be lowered?

 

I had the same problem and it was a busted dome gasket.Getting to much air will cause it to rev higher.You can get a spray to spray around the dome and if the gasket is busted it will haul in the spray and bring the idle down to almost normal.Then all you need to do is replace the gasket,not aq big job only took me around 30 minutes.
good luck

 

if your referring to the round gasket under the air cleaner, mine is broke in half plus the wing nut is missing and i've had aplastic bottle top on for the nut. so today i lined up the gasket as good as i could and put awing nut on. the idle went down to about 1000rpm. i guess i should by a new gasket. thanks for your answer.