Hi,

Sorry for poor English

Please help if anyone have faced this issue or knows how to fix it.

My 2005 ls430 with 88k miles runs fine but the only problem that RPM drops from 900 to 400 only when shifting from P/N to D/R and engine starts vibrating a little bit !!

Any suggestions as i don't want to spend money on something won't fix it.

Thanks in advance

 

Sounds like a vacuum leak. Take the engine cover off and with a flashlight look for cracks and missing connections. Don't forget to check the underside of the hoses, too.

 

Could possibly need to clean the throttle body and idle air circuits. That helped mine.

 

Good advice, clean the TB thoroughly and reset the ECU. Ideally have the TB calibrated via after cleaning. The vibrations you feel at lower rpms are coming through the motor mounts and they do need replacing over time as the rubber deteriorates. Smart to clean the MAF while you are at it and I recommend personally replacing the engine temp sensor at around 90k miles. What I did and all these led to notable performance / efficiency improvements. Oh yea, cleaning the EGR also improves the idle. And heck, why your are it clean that smog sensor too. Super easy.

 

Thanks guys for your help and suggestions , i will try them and will keep you posted

 

i have done everything you have mentioned plus ran seafoam in quarter fuel tank and seafoam spray in TB now idle is good but still i feel car doesn't have power like before and noticed that rpm drops significantly when take off my foot from pedal then it raises back again with no feel of any difference in engine work ,is it normal or it indicates an issue ?

I cleaned it before but it didn't work

I have checked all hoses and found no leak and all the old cracked ones were replaced

 

I still wouldn't rule out a vacuum or evap leak. The only way to tell for sure is to have a smoke test done. Also, I wonder if your VSV might be causing some of the vibration at idle? Seems like more testing is in order. https://www.clublexus.com/forums/ls-...procedure.html

 

These screenshots are taken while my car on operating temperature and gear is on D to show you how rpm drops and to help finding anything abnormal looking at all these values


thanks in advance

 

Mine only idles like at 450 RPM as well when sitting at a red light after the engine is warm. It doesnt vibrate or anything. Only time it idles higher is when i have on the headlights or A/C.

 

Do you think this is normal ?!
As per my poor knowledge, all cars should idle at 600 to 1000 rpm
i believe 450 is low and indicates something abnormal

 

It seems odd that it is so low. But its been like that for years but has never caused any problems. LIke i said if i have accessories running it idles a lot higher.

 

It's supposed to be 800 and if it's not or it alters from having ac or other items on you need to clean the idle ports in the TB and perform a idle relearn.

Reason it drops but goes up if you turn the AC on is the car can see the extra load will cause it to shut off so it uses the throttle blade motor to open the butterfly a little to prevent that. Ideally the idle ports are supposed to provide enough air to not have fluctuation or the blade to need to be involved but once enough build up happens in those ports it can't flow enough.

Any vacuum leak will increase the idle not lower it plus if bad enough will trigger a MAF error code

 

That's correct my friend specially when AC is On , idle RPM will be normal
I don't like to keep my car like this even if it's running fine

 

Probably you need to clean these 8 small holes and 2 larger holes at side.

The purpose of these holes are to provide air to air mix/assist passages of 8 injectors. This box is located at upper part of the throttle body. There are 2 Philips screws and a lid just above this box. In order to clean 2 bigger holes, you need a can of carbon cleaner or more. The cleaning has to be done while the engine is running around 1000rpm or so aiming to have the enough negative pressure and also to prevent a hard engine starting after the cleaning.

These 2 bigger holes are connected to 4 injectors each to provide air for the smooth engine running and the better gas mileage. It would be better to use some compressed air to clean thoroughly.

 

are you sure that rpm increases in case of vacuum leak so i don't need to check it ?