My car after it has warmed up idles at about 500 rpm and sometimes starts to shake a lot like its misfiring. I put high test in it and it got rid of the shaking problem at idle, I guess it was misfiring but it still idles real low. I wouldn't think an idle this low would be normal, does anyone know any possible causes for this. Could I set the idle higher with the iac somehow. Any help apreciated.

 

adjust the idle screw and keep 93 in there