i just bought this truck and the guy who owned it filled up with his fuel out of the tidt tank and i got home with it and filled up with ULSD and since then it was low in drive i heard adding 2 stroke oil can cure this its a 94 cummins apparently the older ones need lunrication please help it was running fine with his fuel and the whole way home

 

When a 12v is cold, they idle lower. It's not hard to raise the idle. Just a 10mm wrench.