i have a lt1, and i started the car the other day, and out of no where, i had i high irratic idle. I tried to adjust the idle screw down, but the idle did not go down, It is idling at like 1800rpm. I think it is something along the lines of a sensor. Does anyone know, what could be the problem? Thanks in advance

 

try the TPS sensor and the IAC. those are the 2 most common.

 

TPS and IAC would be the most likely sensors to cause that, but check for vacuum leaks too.

 

i had that problem too when i put on my 58mm throttle body on my non bored intake and had all kind of surging / high idle issues. now that i got my motor back together with a ported lt1 manifold and ported for 58mm, it idles fine and no issues.