Mr4btTahoe

Hey alls...

So I serviced the wife's car over the weekend ('06 GS300 awd)... fresh denso plugs (which someone apparently was chasing a misfire at some point as they replaced 2 coils and 2 plugs with autolite platinums... other 4 were denso).

While I was at it, I cleaned the throttle body. Got everything back together and fired it up.. took a bit to hit (I'm assuming from having a bit of TB cleaner in the intake)... but after it started, ran glass smooth.

Took it for a drive and when I got home, I noticed that the warm idle is no longer 500-600.. but now ~750 or so. It's dead steady... smooth.. no hiccups or hunting.

What is the actual idle spec?

I also noticed that the 2nd plug on the passenger side bank was running lean... tip was more white then tan. It was the only plug that looked that way which is kinda odd. Ideas?

pbxcomm

Did you set the gap on all plugs to .044?

aristo1987

Oem plugs comes manufactured pre gapped

pbxcomm

Absolutely not "pre-gapped"..
No offense, but if your installing plugs with the assumption that they are pre gapped, you may be unpleasantly surprised when you pull them out and find they are off many thousandths.

There is no such thing as pre gapped plugs, never have and perhaps never will be.

Mr4btTahoe

I dont believe you are supposed to gap iridium plugs as you'd damage the needle like points... not sure how you'd get a feeler gauge in the points being as it has 3 ground straps.

With that said.. I don't see improper gap causing high idle (yet glass smooth). If it was running rough or had a misfire... sure.

http://densoautoparts.com/spark-plug-installation

According to the manufacturer (Denso)... the gap is factory set. I'd bank on it that Toyota didn't take the time to check the gap going down the assembly line. Also says on their website that it isn't recommended to gap them as they can easily be damaged.... but anyways...

pbxcomm

Ok... So you installed the "Iridium TT Twin Tip".. If so, you gap them (center electrode) at .044 with a small copper gauge.. Or, Mitutoyo makes a precision tool for gapping P/N 186-105. Your best to convert the .044 into MM as MM are far more accurate.
Improper gap can cause a high idle (or slow idle).. The larger the gap the hotter the spark (which can cause a lean condition on one or more cylinders). The ECU will read this as lean and raise the idle to compensate as slight misfire. Smaller gap is colder and as such the ECU would read this as a rich condition and compensate as such.
I've pulled plugs from the box and found that a majority were no close to .044 and were all over the map. This is true today as it was as far back as the 70's when I started working on cars.
Tune up 101, never assume the gaps are set from the factory.. If you do, you'll "chase your tail" locating the problem post plugs..

BTW, my GS 350 runs best @ a gap of .046...

Good luck..

Mr4btTahoe

The lean plug was the old one I removed... A factory plug. The car runs smoother then it ever has.

If the ECU was trying to compensate for a slight misfire, it would throw a code for a misfire.

What is warm idle spec? The car could have been idling too low this entire time (which based on how it runs now and the 2mpg increase in economy.. I'd venture to say that it's better then it previously was). Also pulls harder then it has before.

pbxcomm

The engine can have a misfire without throwing a code. The only way to determine if you have a slight misfire is with Techstream.. There are misfire thresholds before the ECU throws a code and these thresholds must be met or exceeded..

750 @ idle is too high and may indicate a lean condition. I would take it to a dealer for diagnostics.

My GS 350's warm idle is between 550 and 600 RPM (normal spec as it was when it was new).

Mr4btTahoe

Hmm... service manual specs 580-900rpm depending on a few conditions...

~580 rpm in park/neutral with AC off and at temperature.

~650 rpm in gear with AC off

~750 rpm in park/neutral AC on...

~900 rpm in gear AC on.

Before changing the plugs and cleaning the TB... the car always idled at 500-600ish and would stumble from time to time. I'll have to check but I'm curious if the AC was one as previously, it would not increase engine rpm while it was.

I'll also pull the plugs and get a reading on them... no point in taking a car to the dealership. I can easily monitor fuel trims, etc.. on autoenginuity along with "slight" misfires.

The car previously had mixmatched plugs (different brands/types/etc)... and idled ~550ish all the time.

Anyways.. I'll get time over the weekend, I'll pull a plug from each bank and see how they are burning and go from there.

93SCMax

Sounds like you are where you need to be...I'm assuming after the plug change you were in neutral, AC on. I'd think the original low idle was out of spec low because you had mis-matched plugs. You did yourself and your wife a big favor by changing them out with the Iridiums.

Thanks for sharing the multiple service manual specs. I checked my owners manual after your first post, and couldn't find a low idle anywhere. I'm curious if there is a different spec between the RWD and the AWD? I have a RWD and 650 rpm in gear with AC off feels about right to me.

Mr4btTahoe

It took forever to find anything published with the specs... finally found an online service manual for the engine (not the car) that had that chart. I'm still going to pull the plugs and check how they are burning. It's the fastest and most accurate way to determine what is going on. If they are not tan... there is an issue somewhere. Dark or black is rich or burning oil... White/grey is lean. Light tan is the butter zone. I could put my wideband on it but I dont really want to go to the trouble.

Oh... and the GS350 does have a different engine so idle specs may be different. The '06 GS300 is the only year the GS used the 3gr-fse... reason being is the direct injection only system leads to heavy carbon deposits on the backsides of the intake valves and intake manifold... eventually will cause a misfire from lack of compression. Only way to fix it is media blasting (with heads still on engine in the car) or hot tanking the heads after removal. Lexus was offering to rebuild the engine for free for quite some time due to the low tension oil rings adding to the issue... but the problem will still come back. In '07, they changed the engine along with the injection system to incorporate direct and port injection. Port injection keeps the valves clean and all but eliminates the problem while keeping the benefits of direct injection.

pbxcomm

You may want to perform a compression check on all cylinders while you have the plugs out.
I believe normal compression is 190 - 199 lbs with a tolerance of no more than 15 lbs difference per cylinder.

Mr4btTahoe

Apparently it just needed to relearn the idle after cleaning the TB... as it idles dead nuts on spec now with not so much as a hiccup... (~580-600 in gear with AC off).

I suppose I should have unhooked the battery to clear everything out so it could go through the process faster but oh well.. all is fine now.

93SCMax

Good for you. Thanks for reporting back.

YxUxMADDDD

iTrader: (2)

Nice to know........