Weird o2 sensor readings

[William Shore]

2001, Tacoma, regular cab, manual, 2.4l.

I’ve been trying to fix my high idle problem lately. I have to CEL or codes. At first startup, the engine will shoot to 1500-2000 rpm’s then settle at about 1200. After a couple of minutes, it will reach 1000 and stay there for a while. Sometimes when it’s warmed up it will come down to 850.

I cleaned my MAF and IAC. This didn’t help. I checked my TPS, MAF and ECT according to the FSM. They seem fine.

I have a Blue Driver OBDII scan tool. I used it to watch MAF, fuel trims and o2 sensors. The MAF seemed to work properly and the fuel trims looked to be ok except for my short term reading of -6.3% at idle. My long term was pretty steady at +0.8%. Now is where things get weird. My upstream sensor stays at a high voltage all the time and barely moves and my downstream moves with the throttle (I’m not sure if this is abnormal behavior for the downstream). The upstream does move with the throttle, but just barely.

Please someone help! The only thing I know to do is replace the IAC and o2 sensors, see if this fixes the problem and work from there.

Below are two videos of my live data. The first video is just idling and the second is idling with some blips of the throttle (when the o2 sensors’ readings change).

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[William Shore]

***UPDATE***

So in my research, I saw that o2 sensor data should be looked at when the engine is at 2000rpm so here are two more videos.

The first is running at 2000rpm steady and the second is idling then bring rpm’s to 2000 and holding (when curve shoots up then gradually comes down).

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