87 Blazer 2.8L failed smog test - high idle?

[lhspatriot3]

I recently ran my 87 S-10 Blazer (2.8L, TBI, 45k on rebuild, w/man. trans. thru Wash. States wonderful smog test and failed (HC emissions too high at idle and cruise speeds). I noticed that it was idling pretty high (1100 rpm according to the new high tech smog machine I was hooked up to and my tach.). I have since done a tune-up (plugs,cap,rotor,air filter) and cleaned the IAC valve. It still idles too high, when fully warmed up. I need to run it thru the test again, but before I do I would like to try and fix the high idle problem. I need some ideas on what could be causing the high idle and what I can check? I assume the high idle is related to why I'm failing the test. It seems to run fine other than the high idle.

[JOEROC]

First check for vacuum leaks, use a can over carb cleaner and spray it around the plenium when the idle is high, it could be warpt and expanding when the motor gets hot or a bad gasket,check all your lines to,also change the oil and filter thats helps it to pass the test also. hope this helps

[JOEROC]

oh when you spray the carb cleaner listen to the idle it will change if its a vacuum leak. if its the
plenium try to snug it up . dont crank on the bolts you dont want to snap them off.
if plenium is warpt you can double up the gaskets
to fix the problem. cheaper then buying a new one.

[tom3]

Two things I've run into. Thermostat going bad or temp sensor out of spec, computer sees cold engine and adjusts for that. ECM has a different sensor than the gauge and the gauge might read normal if it is the sensor. Also check the vacuum line down to the air pump, has a rubber end there and breaks off sometimes.