Updated... here is some basic info:
Poor idle can be caused by a number of things. You should always check foro the cause in this order (order of probable cause):
- Old, worn plugs (replace)
- Old, worn distributor cap/rotor (replace)
- Old, cracked wires (replace)
- Valve adjustment (too tight will lower idle)
- Vacuum leak (check hoses and IM/TB gaskets)
- Air in coolant causing thermal valve to oscillate (properly fill & bleed coolant)
- Funky EGR valve (clean or replace)
- funky EGR port in manifold (clean)
- IACV dirty (clean)
- TB dirty (clean) --> remove MAP sensor first!!!!
- Dirty injectors (should send them to someone like RC to be rebuilt)
- Defective fuel pressure regulator (check for proper fuel pressure)
- Primary 02 Sensor (if fouled it can lower idle speed)
- Bent valves (do a compression test, then leakdown if bad, repair head if valves leak)
- Bad MAP sensor (try giving it a thwack w/a screwdriver handle)
If you have messed with any of these recently, start there first.
The idle adjust screw is the LAST thing you should look at or adjust! The idle speed is controlled by the ECU and set properly at the factory. There are no bolt-on mods that will affect idle speed. Only a valve adjustment, new TB, IM, blower, turbo, or internals should have an effect like this. Fix the root cause and you won't have to dick with the idle adjust screw.
Some more "case study" reading:
Rough idle and vibrations
older threads:
moderate problems:
Idle
bigger problems:
Car stalls when coming to stop?
You should be able to search any of the items listed above and get plenty of information on how to fix/address these issues.