My truck is idiling about 400 rpms and it dies if you let it idle very long and it is also running rich. I have cleaned the throttle body and my intake is good not leaking. I was thinking it could be the upstream o2 sensor so today i unplugged it and started the truck and there was no change in the idle. So could it be bad? Any help would be greatly appreciated. It is a 1996 4 wheeldrive with the 5.9 it has 160000 miles on the truck and exhaust including the o2 sensors and 68000 on the motor and trans.

 

can i ask a question? ...have you done anything to the motor before the problem...reason being is to know if what i say is right ....or wrong....anyhow ...spark plug wires?? //plugs? running rich without vacuum leaks would mean bad o2 sensor like you say or not good spark..i think

 

Could be a bad O2 sensor. If you give it gas, does that help it stay running (until it returns to idle, of course)? If so, I'd also look at the IAC.