there is a problem with my idle, at first it idles just fine at about 800rpm but when i let it sit and idle for anything over a half an hour then it starts to misfire, more and more the longer it idles over a half an hour, and eventually at about 45 minutes of idleing it goes into limp mode where there is no power at all and it sputters until i really get on it hard and bring it back into regular running order, now ive checked my codes and they said rear o2 sensor i replaced both and i got no check engine ligth and never have but it still does it, what do you think is the problem? i have 156k miles and it just started happening at about 150k miles
thanks

 

I would try cleaning the ideal air sensor on the throttle body. If that don't fix it replace that sensor..

 

idle air sensor? whats it look like?

 

If your standing on the driver side looking at the throttle body, it will be on the far side of it. 2 torq head screws and a 2 wire plug.

If you pull the air intake tube off the top the throttle body you'll see a slot on the far side that will also need to be cleaned with some carb cleaner also.

Hope this helps you..

 

when you take the IAC out be very carful when cleaning it as you can mess it up. Also if you can check fuel pressure when it starts sputtering if you have a gauge.

 

I'm with OKC. Sounds like a fuel pump going bad to me. An early symptom of a fuel pump going bad is they start to lean out pressure when they get hot. About 30-40 minutes of running....or after 30 minutes of running if you shut it off it won't start back up until it's had time to cool.