UPDATE!!!!
Well I replace intake purge gasket as well the upper intake plenum gasket. Waiting until Tuesday February 18th to get the throttle body gasket. I removed the throttle body just to find little issues. Like the couple little cooling hoses where cracked and another surprise. The tps was not properly sitted in place. Obviously a leak there. I notice this cause when I took the car to car wash the car act up when water hitted this area. Anyways I put some rtv sealer around the base of AICV. and like I said on earlier post the connector for the vvt solenoid for bank 1 was ruinned. Fix that. I will update on Tuesday or Wednesday about the results. Hope I don't have to replace the exhaust manifold gaskets. I know will be a ***** , thanks

Well I did not replace manifold gaskets. I did some another little things. But the CEL came on again. The system too lean bank 1. FML!!!
Took it to a mechanic. He says if O2 are new and all is seal besides manifold gasket it's the cats . Omg÷! At least I found them online for 182.00 each not too bad. See what happens later down the road

^ yo what is the part number for the throttle body gasket?

Hey wazz up a throttle body gasket ha. Idk. I didn't bought oem gaskets.
I just went to auto zone and u ask for them. They will gave u the ones u need. They have pictures of them so u can choose the right one.. easy. Brand is felpro.
I got 2 boxes. 1 for the intake plenum gasket and another little one for the throttle body. 61281 felpro part # for the throttle body gasket. Let me know if u have another concern.

UPDATE!!!
Had the p0171 coming back again. But I was a little frustrated not to know WTF was going on after all I did to the car. Decided to get a odd scan tool online.
Got it today. Did all the scanning through all the sensors and everything came out good. Honestly some reading like más sensor wish to know what's the proper readings. I do know the reading the my sensor is putting out but don't know if It s correct. Honestly I feel the CEL it's cause my big *** filter and and the maf is detecting way more air coming in to throttle body??? Maybe . Any was I did discover what I though was really low idle was to me normal. In park position I'm having 750 rims and drive I'm having 500. I think is normal but on the tachometer I'm showing way less like 200-400
Anyways if if the code comes back I'm gonna put a smaller filter and see what happens. Glad I bought this obd scanner. Only 12$ and I bought the pro app versión for android for 4.99$ wich tells u live data.
Now I have peace of mind the nothing is wrong with car so far. Thanks

That sounds good bro! Get that done and let us know what happens. I hope everything turns out alright. Don't worry, once you get the problem nailed, you'll be happy you stood with the car.

You do know if you buy the cheap aftermarket cats, this problem is prone to happen again in the near future. I'm just sayin. Get it installed properly and put DOUBLE GASKETS on each cat wherever you can fit it. Put spacers in between the nuts & bolts as well. Best way to avoid leaks and escapes.

Yeah i been learning a lot about sensors and readings after I got this obd2 reader. I been having a last conclusion the my problem is either my gas pump. Filter or maf sensor. I been watching all the readings. My light comes on on high rpms. So it means maf of fuel pressure. I will be updating for any changes. Thanks

Good luck bro! Keep us updated!

what is considered "normal" idle for GS400. My car doesn't idle extremely low anymore after replacing the TB however, i noticed it still idles around 400-500 at normal temperature. My sister's 3.5 honda idles around 700. It just bothers me when it's around 400 because once it goes down to 300<, the alternator doesn't charge anymore.

Yea well got the conclusion there's nothing wrong with the car. Just my big *** cold intake. O2 ' s are new so they re expecting to read the oem air quantity it's going on throttle body. It maf it's detecting way more so maf reads the extra air as a rich lean condition. I'm not going to worry anymore about it. I have to learn to live with the light. Thanks

Hi why did u replace the tb?
Anyway before I start working on the car with this issue , what really make.my idle to get better was a new battery and new O2 sensors. Why . Don't know just see that difference.
Before my car idle at 300 or 400
After all that and several gaskets and miscellaneous I did. My idle is between 500 - 560. Period. And if I turn my headlights in it goes up to 600- 650. I know exactly readings cause I have a reader where u can see live data. . As u can see i'm in idle stop.on drive on normal temp and I have 512.rpms . Let me tell.u the rpms on the car are not accurate.i confirm that. So If u guest u have 300 rpms u may have 400 or little over. Let me know if u have questions

Well, i replaced the TB because at normal temperature my car would idle 200-300 RPM at redlights. Eventually, the alternator would cease to charge the battery due to timing and idle issue. Car eventually runs only on battery until it depletes and stalls.

I always keep my headlight on even during day time just to keep RPM above 500 to have car run normally.

Replacing the TB seemed to have solved the low idle issue, just that it's still around 450-500 range and it scares me.

I apologize, I didn't read every post on this thread, but have you looked into oil control valve?

https://www.clublexus.com/forums/per...ve-filter.html

http://us.lexusownersclub.com/forums...gh-idle-fixed/

Oo I see well my rpms are around 500 and I'm good with that. As longest don't goes lower than that I'm good. And for what I know that's the normal rpms range. ?? That's what I hear. Keep us posted