6.2 diesel idle

[86c20]

so i got my new 6.2 in and running but it seems to idle high. all the time. now i have unpluged the fast idle wires still high. backed out the idle screew still high. but pull back on the throttle its self comes down to where i think it should be. no working tack yet. i think i have the return spring in the right spot.

just for numbers and a guess. i would say idle is around 1000 rpm

also she will rev up on her own then come down for a bit then back up. its slow but it is a good 500 rpm jump.

i know my fuel is old and i know it is a mix of wast oil and diesel. close to 50/50.

any help would be great. thanks