You are not supposed to ever adjust them because it's an emission
part. Here's what I would do based on what I did on my 88 Mustang
5.0.... First, do NOT back the screw off and then start fiddling with
the throttle and moving it open and closed - you will make the plate
dig into the coating on the throat and you don't want to do that. Just
back the screw out till it no longer touches the stop, then turn it in
very slowly till it JUST BARELY touches the stop. Then turn it in
another half a turn, this will crack the throttle open slightly. Then
start the engine and see if it seems to be running ok and maintaining
proper idle speed. The Idle speed bypass valve will, if it's working
right, adjust the speed to the correct setting. If it is not able to
maintain a uniform idle speed then turn the screw in another half
turn. (turn the engine off, add the half turn, restart the engine)
Even with a new Idle air bypass valve on my 5.0 this was the only way
I was ever able to get it adjusted so it idled properly. There is a
factory procedure for the mustang that I tried first (used a feeler
gauge, don't recall the details) but it would not idle properly when
adjusted according to the book procedure.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.