Idle issue, O2 sensor

[JustinGTS-T]

Hey everyone!

I have had a rough idle for sometime now, typically sits at about 900 Rpm and fluctuates constantly to 600 Rpm when car is cold. I replaces the O2 sensor last year with no real improvement, replaced plugs and gapped, replaced Maf, adjusted TPS ect ect ect. Car does run rich from the stinky tune, I just disconnect the O2 and the idle stabilized and is as smooth as can be. Now typically I would say " let's replace the O2, however this is a new o2 with probley under 5000km and it didn't fix the initial issue. Any ideas??

[Supraclean]

Sounds likes a boost leak to me.

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[Skym]

Could be an airleak somewhere. If engine is running rich it can foul the o2 sensor.

Revs can fluctuate alot when o2 sensor is stuffed, have a intake manifold airleak on head to intake manifold flange (o2 sensor + ECU make revs fluctuate up which is running lean and down which is running rich), AACV is not adjusted correctly (ECU, AACV should be both set as say 650rpm for RB20DET) or is dirty. Sometimes AACV needs to be replaced. Plug o2 sensor back in and unplug AACV (stops ECU playing with idle rpm). If idle stabilises, then AACV might not be not adjusted correctly.

Also rough idle can be related to running too thick oil and engine struggles to idle. I found this out when switching from 10w60 to 10w40 oil and idle was smoother. Factory is 7.5w30.

[JustinGTS-T]

My bad it does it when it's hot, I don't suspect it would be a boost leak as I'm not producing boost at idle. The car pulls a 16-18 inch vacuum at idle as well, I'll take a look at the AAC possibly a bad O2 straight from the box?

[JustinGTS-T]

Just disconnected the AAC at full operating temp and it almost stalled, so I know that's good. I replaced all the vacuum lines, and the PVC valves don't appear to be plugged ( no dipstick popping out.

[jinglebell17]

Just disconnected the AAC at full operating temp and it almost stalled, so I know that's good..

Thats strange cause my IAC valve is stuck open and my car idles at about 2,200 RPM when its connected. When mine is disconnected, my car idles at 1,100 RPM strong (it idles high because of setting on my S-AFC) ... Anyway Ive been driving around with my IAC valve disconnected for about 2 weeks and my idle doesn't fluctuate and my car definitely doesnt stall without it connected. I dont think that helps your problem though.

When I got my car, the idle was fluctuating, then it got to a point where it would just stall more often than not. I took out my MAF sensor and dump carb cleaner through it and then took a long skinny hook and shoved it through the screen and cleaned the wires on the inside of the sensor. I literally scraped a good couple chunks of gunky dirt off the wires, then I slapped the MAF sensor back on and my car hasnt had an idling issue since... Well other than my IAC valve is stuck open now but whatever its unplugged