I have a big problem with an 88 ranger with v6 automatic, 2wd. The oxygen sensor keeps going bad...I have had all kinds of test run on it and it keeps showing the O2 sensor is bad. This is the third one I have put in and I am holding the forth one in my hand waiting to find out what is really wrong with my truck.

It is not keeping at an idle speed and continues to die. The engine light will go on and off..at one point it got to where the truck would not start at all. I changed the O2 sensor and it started right up, but is still not keeping an idle speed and dying. When changing the O2 sensor with less than 100 mile on them it is solid black with pretty bad carbon buildup.

Within 4000 miles the truck has had a major tuneup, along with new heads.

Sorry for the long post, but I am all out of ideas to fix the problem.

Thanks,

Jason

 

There is an IAC valve, Idle Air Control Motor mounted next to/on the throttle body, looks like a tiny can, a large D cell battery, with two wires and an oval flanged mount with tho bolts. This adjusts airflow to correct the idle. You can tell if when you crank the steering wheel to "lock" position at the end the idle should go up a little, also, with the A/C on the idle should change if it is working properly.

This can usually be taken off and cleaned, don't use carb cleaner, use Fuel Injector safe product. From your mention of carbon buildup this may be clogged.