idle surge

I recently had a check engine light come on, and the idle would drop like it was going to stall, then bounce right back to normal. It does this time to time with no light, but now it threw a light. I checked the blink codes with the 2x key switch cycle procedure, and got a 12, a 21, and a 55 indicating end of codes. In that order. I'm assuming it's my o2 sensor (code 21) since I disconnected my battery recently (code 12).
The engine has always had very intermittent strange idle symptoms. Recently upon startup on a cold engine, the rpms would be high, and only come down when I bump the accelerator pedal. I cleaned the throttle body and replaced the tps and iac valve a few months ago. But, I'm wondering if since my o2 sensor was going south, it ran rich and gummed up the iac valve and throttle body again? Thoughts?? Another clean out?


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id start with swapping that o2 sensor. it sounds like its trying to read it and cant adjust to its readings. and going back to open loop.

Tacowhip said:

... wondering if since my o2 sensor was going south, it ran rich and gummed up the iac valve and throttle body again?

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Have you tested the O2 sensor ? Did you install a cheap crappy Chinese IAC with a "Lifetime Warranty" ?

The O2 sensor can't gum up anything, if the throttle body or IAC is dirty, there is likely excessive blow-by.

I did not test the o2 sensor. I am very familiar with a meter, but do not know how to test this sensor. Any help would be appreciated.
I bought the IAC and TPS sensor from napa auto parts store by me. They were about $45 each. I've always liked napa parts. No problems with them in the past. I'll open the throttle body when I get home and check it out, but I'm leaning towards a bad o2 sensor


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