my 1990 turbo mx5 wont adjust idle when i turn the screw on top of the throttle body. im sure it is the right screw, it has the little plastic black cap over it and ive seen tutorials on how to change it, but the idle remains a constant ~500rpm which is too low for me. the highest it will go up to is about 600 rpm, so it kinda works, but i would assume that i can adjust it higher right? anybody have any idea of what could be the problem? thanks. it is manual btw.

 

Do you have megasquirt or something other than stock? If so...NEVER TOUCH THAT SCREW.
Think about it. If it idles fine before you mod something...and then you install something like a megasquirt, and now it doesn't idle right. Your idle screw is not the problem...it never is, never was.
Idle screws are for Delorean's that have flux capacitors. Come to the future where idle screws don't get touched...because no carburetor.

 

it is on bandaids, stock ecu, it has had this problem ever since i bought it.it drives ok, just idles too low for me

 

I believe you have to jumper something in the diagnostics box while you turn the screw. Would have to do some searching on m.net to find what to jump.