My check engine light came on a week or so ago. When the truck is in gear it begins to idle very poorly and will sometimes stall. I went to Advance Auto and had them read the computer. It said Lean Bank 1, Bank 2. They then sold me 1 each front and rear 02 sensor. When I got home and began to work on the truck I found that there were 2 upstream and 2 downstream sensors. I replaced one of the upstream sensors and went back to Advance, had them reset the light and returned the downstream sensor. I, of course, did not fix the problem. When the check engine light came back on I went to AutoZone and had them read the codes. They came up with, Lean bank 1, which came up twice. I replaced the other upstream sensor, had them reset the computer and when the light came back on had them read the code again. This time they got the same reading that Advance got which was Lean Bank 1 Bank 2. Since replacing the upstream sensors did not fix the Bank 1 problem, I can't believe that replacing the downstream is going to be of any help either.

Any ideas on what might be the cause of my rough idle?

 

Normaly not, the only thing the two rear o2 sensors do is monitor how much emmisions go through the system they don't change the amount of fuel like the upstream o2 sensors do. It's rare that they go out. but they could and give a false reading to the CPU. The rough Idle is probably caused by the IAC sensor, it is behind the Throttle body, remove it and clean it up with carb ceaner or intake cleaner if it works better after cleaning then you need to replace it . the cleaning is only a short term fix.

Lance

 

Because of things that I had read in other threads and after a conversation with a friend of mine that had a lean reading turn out to be a broken intake manifold, I started the engine and began to run my hand over hoses listening for a change in sound. I found an elbow up under the manifold that was nearly in 2 pieces. I paid the Ford dealer $14 for a new rubber elbow and it seems to have fixed the problem. I think the reason for the high price of O2 sensors is that they are always recommended to fix a lean problem but are probably never the cause. It is the parts manufacturers plan to stay out of Bankruptcy. I'm just glad I could help them out.

 

O2 sensors normally last up to 100,000 miles. But if there is a fuel problem, like burning to much it will burn a O2 sensor prematurly. Glad you found the problem. remember the codes point you in a direction it does not mean the prblem but you still have to troubleshoot.

 

Replace the IAC valve. It'll run fine.

You'll have to replace the egr valve soon,
it usually follows right on the heels of the IAC
in my experience. Take the throttle body apart
and cean the egr ports of carbon build up
where they met the egr valve. Good luck.