rough idle /skip

[dsltch]

have a 99 powerstroke...has been sitting awhile....has skip at idle...if I hold throttle at 2k it will smooth out....ran the scan tool on it and came up with icp ckt low...came up with .22v at koeo.....checked the fuel and it was black...changed out filter and added some 911......still skip and throtlle respone is bad till you hold it at least 1/4 way down....can hear the cylinders cut in and tach will go up.....not to familar with the 7.3 ih.....any help and test ideas would be great....I am going to do the injctr harnesses nder the covers....truck only has 160k on it