i have a 1999 4.6 with the rough idle.. ok took to the dealership... they checked it out... said it was the idel control valve... they changed it... got in the truck to drive it home.. it was idleing bad.. went back in there before leaveing and told them it was not fixed.. when i would put it in gear it would idle down too much and die... he said it is normal for it to idle down... i said yeah to idle down a little but not to die.. i bought the truck three weeks early from them... he said we changed the idle controll valve... and that is supposed to fix it.. i told him that it did not fix this one that i wanted it fixed.. anyways they checked it out agian.. now they say it is the main processor in the computer... they are going to put a new computer in it and we will see if that fixes it..i will keep u posted... they have to order it it will be about 5 days to get it..