Just thought I'd lend my experience in case it could help someone else. Had intermittent very rough idle. Checked many things. Cleaned fuel injectors twice (once at dealer, once at independant shop). New plugs, checked cap/rotor and wires. Finally changed pre-cat O2 sensors and cleaned grounding point to frame. The grounding point to the frame is right under the condensation drain for the air conditioner on my truck. Don't know if it was the O2 sensors or the ground cleanup, but it runs much better now.
CK5
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7.4L Vortec rough idle
- Thread starter sandy78
- Start date
It was most likely the o2 sensors. Did you use an obdII scanner before doing any work? When mine had this problem I could visibly see the fuel trim was waaaaay out for the #1 bank and then checked o2 sensor readings and could see the #1 bank #1 sensor was way off.
I did scan them and they looked fine and tested fine. I kept having a P0300 come and go (every few weeks), then I got a "insufficient switching S1B2" for a couple days-- I think it was code P1143. That's what made me finally change the sensors, even though they looked okay. A buddy of mine at an emissions station told me to check the ground, so I did that at the same time.
