Ok so I just got this truck and when you first start it it runs really rough, especially under a load (going up a hill). Once it's warm, it actually runs pretty good. I have already replaces the idle air control valve because it has shown a code for that but without resolve. Any ideas? Fire away! Thanks in advance.

 

Try unplugging the pre-cat oxygen sensor to force the PCM to stay in open loop mode. If the rough running doesn't come along while the thing is unplugged, replace it. Use only a dealership part, Denso, or NTK. Any other is more likely than not to disagree with the PCM's slow feedback loop.

Also: Don't let the thing running well without that sensor fool you into thinking that you can just run without it. You can, true, but you won't like the result.

 

So, when I unplug it, I should expect it to run rough correct? If it doesn't change then it's bad? Did I understand you correctly?

 

It's the other way around. If it doesn't run rough with the sensor unplugged, the sensor is bad. Oh, yeah: Expect a CEL and code for the sensor when it's unplugged. Just clear it later.