Messing around with my 09 LS today. Turned the HVAC off, put in Drive with foot on the brake. Idles rough and around 500 RPM. Put in reverse and idle, with foot on brake is perfect at 750ishRPM. Turn HVAC on and idle is smooth as butter in drive. I know in old days there was a solenoid that would kick idle up on carbuerated cars when the AC compressor was activated. Obviously there is a big draw on an engine with compressor running. Not throwing any codes but would like to know why low/rough idle in drive but not reverse. Thoughts??

 

You have a vaccum leak somewhere, check for oil leaks since that will cause a lack of sealing for the PCV and MAF metering. If you are 100% certain there are no leaks then clean the TB and perform a relearn

 

Thanks Striker. Odd though that it does it only in drive. I just did the valve cover gaskets, HPFP gaskets/seals this weekend. I was leaking oil badly from the HPFP and the valve covers and that has definitely been resolved. And it was doing it before I did any work. Maybe a smoke test is in order.

 

Yep that's exactly when it will do it since the engine is under load in gear like that, if you just fixed everything then I would say just do the relearn and it should be okay. Do it with the car hot not cold btw

 

Good stuff, thanks. Any guidance on doing a "relearn"? I just bought the $750 XTool D8 trying to figure out how that beast works. Wanted to do a ECU wipe on the transmission so that could do a relearn. Having some odd gear hunting and was suggested to clear adaptations. DOn't have techstream and seems like a PIA to configure and use. Will keep this post updated accordingly.

 

Honestly no clue, I use Autel and Snap-on tools form most stuff and I have a copy of techstream and VCDS plus VAGCOM for my own cars.

Let me know how it goes, at a brief glance it looks like the tool you linked should be able to take care of it for you.

If you don't mind, test to see if it can really do keys like it claims.....I'm currently eyeing a 6k key programmer but if that one can actually do what it claims that would work for my uses.

 

A while ago I noticed a similar low idle issue on my ‘07 and looked to some old forum threads for information. Here’s an example : https://www.clublexus.com/forums/ls-...-low-idle.html
it seems the LS will low idle if the electrical system is not under load. My LS will low idle in drive if no major electrical draw is present. Seems many have noticed this issue. One past thread responder (can’t seem to find it now) suggested that the car was designed/ECM programmed to run with driving lights on and or similar electrical load causing this low idle response at times.
May just be a programming bug, and not a repairable defect. Just a thought. Good luck

 

A follow up-I have not done a smoke test yet, still on my list. I have realized that it doesn't do the low idle/ac off every time. But, the other day, car warmed up, come to a stop light. Turn off HVAC, idle goes to 500 and a little rough. I turn on the seat heater and bang it pops to 750/normal RPM. Tried this a few times using other electric loads and same thing happens. So, there is something tied to the ECM/alternator/electrical load. Just don't like that it idles rough with no loads and in drive. Seems funky to me. Any input?

 

Yes, have it relearn when hot with everything off so "normal" becomes 700 rpm with no loads and when loads come into play it just keeps it there. I had to do this with both my 430, 460, and Jeep

 

Not sure how you go about the "relearn". Anything specific that has to be done?

 

Yeah, idle till you are at full operating temp after you have confirmed no oil/vacuum leaks with a cleaned TB and then via techsteam/a dealer level tool perform a TB offset relearn. It will allow it to always stay at 750 rpm +/- 50 or so no matter what you have running/not. As the car get older it start compensating for various non-normal states or dirty TB conditions so if you want it to act like stock you will need to clean it up and seal it and have it relearn to stock normal.

 

I owned a total of six LS460s and currently have two and all did exactly what you are describing above. There is nothing wrong with the car, this is normal.

Car is designed to operate optimally with AC on. I would just leave it alone and enjoy the ride with AC on if low idle is bothering you.

 

I don't think this is normal. My 07 never did this and my 2014 didn't do it when I first got the car but it's doing the same thing now. Idles in neutral at 750 but as soon as I put it in D or R it drops down to 500 and is a little rough. A/C on, or seat heaters on and it comes back up to 750. Dealer hasn't got a clue!

 

The throttle blade has a set position it rests at when at idle, if carbon builds up it doesn't have as much airflow resulting in the RPM drop when you put the load of the transmission on it. It avoids this with the AC/heated seats since the program knows demand will be high and it actually adjusts up off the "idle" position unlike when you put it in gear, this is why I am telling you to clean it and have it relearn if you want no load in drive/R to be correct.

 

RPM in ls460 is ECU controlled, when there is any accessory load on the alternator (e.g. AC, lights, seat heaters, etc.) min RPM is raised from 500–>700-750.

My experience is smoothness at 500 rpm varies from a car to another. This is why many people pay attention to this phenomenon. When it is rough people raise concerns. When it is not rough, we don’t pay attention.

bottom-line, I agree that cleaning throttle body and MAF may improve idle smoothness at 500 rpm but all cars I owned dropped to 500 with no accessories.