tekkie

Hello everyone. I have a 2007 GS350 AWD with 235692 km (146452 miles). Recently my car has shut off on me 3 times within a 4 weeks period. In all 3 cases the car shuts off when it is at stop and in the shifter is in "D" and the engine is at operating temperature. If I wait about 1 minute and restart, the car would starts up again and I can drive it normally. When in "D" at resting, I noticed that my RPM is around 500 and I feel the car vibrates. If I put it in neutral or park, the RPM would go up to around 600-700 RPM and the vibration stops. I have brought it to a Lexus dealer and my regular mechanic and they cannot find the culprit. Just to rule out the dirty throttle body, my mechanic re-cleaned it (the throttle body was serviced about 19,000 km ago).

My car has been regularly maintained according to the maintenance schedule and I use only synthetic oil and premium gas.

Has anyone come across this issue? what should the idle RPM be for our car?

Any help is greatly appreciated.

SILENTM

It does sound like a throttle body going out, since that is what controls your idle (700rpm). Have they checked air filter and cleaned the maf sensor. May need to try a throttle body recalibration with factory computer/ techstream

ibidu1

iTrader: (1)

Pretty tricky! If you have a friend with good scan tool you can datalog the motor to see exactly what the sensors are doing and how they are reacting.

I personally wouldnt dump any money fishing for a solution, wait until the problem gets worse. Have you ever tried a top engine clean? Maybe buy a full can of seafoam and run that all through the top intake manifold vacuum plug, with the engine hot

tekkie

Is that normal for the throttle body to go at this mileage? This sounds like an expensive part to replace. I check and replace engine filter as a DIY every 24 KM (~15K miles) and it was repalced last November, 2016 (~18 KM ago). I don't think the MAF sensor has been checked and cleaned; where is this located? I will call Lexus to see how much it will cost to recalibrate the idle. This was also a suggestion from my mechanic. Thank you very much for your input.

tekkie

Unfortunately I do not know anyone with a scan tool to record the motor data; would a regular shop have this kind of tool? Right now I am a little nervous to drive the car since I have read some of the IS have experienced the engine shutting off while driving on the highway. Although in my case, it looks like it only shuts off while at rest. Right now whenever I come to a stop, I would put the shifter in neutral to bring the RPM up. Any idea why the RPM changes when I do this?

XxGoKoUxX

When your transmission is under load, the idle will drop down lower, as it is in gear and ready for movement. When you take it off and put it in neutral, it's the same concept as putting it in park. That will take your car off the driving gear and your car will idle back up.

FWIW, your MAF sensor is on the intake lining (follow your intake tubing from engine to filter until you see a plug, where that plug plugs into, your MAF is located there.

Like ibidu said, the best way to diagnose what the root problem is, is to data-log your car and see what is really happening under the hood.

tekkie

I saw this SeaFoam product at the store and picked one up. Is this what you are talking about? One of the instructions is to add it to a full tank of gas; is this a safe product for our cars?

tekkie

so I took out the MAF sensor and gently cleaned it with a "Q" tip; there was a lot of black stuff. After the MAF sensor was cleaned my RPM went back to 600, although the car still idles rough. For 4 weeks, I did not experienced any engine shut-off until last nght, so the problem has not gone away. I also noticed that when coming to a stop my RPM bounced around a bit before coming down and just when the car stopped, the RPM would dips down to 500 beofre bouncing back to 600. Is this normal? I did not noticed this behavor on my RX330.

My mechanic says I may need to replace the throttle body, but before I do that is there anything else I can try? I do see that there are quite a lot of used throttle body on eBay, is this an option?

ibidu1

iTrader: (1)

Yes with the engine hot, pop off the top engine cover. Buy or find a small vacuum line that will fit on the top intake manifold plug. Pour a small amount of seafoam in a cup and with the engine running at idle dip the vacuum line in the cup of seafoam but dont let it suck to much to where the engine chokes out. You will see lots of smoking coming out of the exhaust keep doing this until you use up the whole can. You can buy another can and put partial amount into the gas tank.

tekkie

First of all, just wanted to "thank you" for helping me out on this. I did not do the top intake manifold as I am not an advent DIYer. I just poured 1/2 can of Seafoam into a full tank of gas and took it for half hour run on the highway. I could sworn the engine was running alot quieter. However, when I got home I put my car in park (engine still running) while I check my tire pressure and the car shuts off. When I tried to start the car, the dash lights flickered and went off and the car would not start. After a second or so all lights would come on but the engine is not running.

I then tried to start again and give it a bit of gas; the engine would stay on but no dash lights. If I immediately out the car in gear (R or D), the dash lights would come on and the engine would stay running. As soon as I put the car in Park, the engine would shuts off. This is repeatable. I doubt that I have damaged something by running the car with Seafoam?

I've recorded a video of this, but it's about 100 mb so I can't upload it here.

RXGS

iTrader: (2)

You said you cleaned the MAF sensor with a q-tip? I’m pretty sure that’s the last thing you should do as you are simply supposed to spray them with a cleaner and let them dry. Try finding a replacement sensor, on eBay as cheap as $20, and see if it helps as actual contact with the sensor could have had a negative impact on the air/fuel mixture ratio

tekkie

Thank you for your help on this. When I cleaned the MAF sensor, I did not touch the "little red glass bulb"; I just cleaned the 2 metal strips on each side. This was 4 weeks ago and it did helped to bring the RPM from 500 to 600. The car ran without an incident for 4 weeks until last Friday. If my cleaning the MAF had caused more issue, then I think I should have seen something worse than what I have right away wouldn't it?

If a used MAF sensor is not that expensive, then I will try your recommendation. Thanks again.

RXGS

iTrader: (2)

Ah alright my mistake. I guess my train of thought behind it is that if the condition improve through an improper cleaning, there is clearly a correlation between the condition and the sensor. For $20, its worth the gamble. Also, when was the last time your spark plugs were changed as at 146k miles, you should technically on your 3rd change. As others have said, I hate the idea of throwing parts at the car, but I guess you need to start with the basics. Hope you get it figured out.

As others have said, a video would be a tremendous help.

tekkie

I changed my sparks plugs at 96 KM intervals as recommended by scheduled maintenance, so the last time I had it done was at about 192 KM and my car is now at 236 KM. I used Lexus original sparks plugs in all cases.
I looked up MAF sensor on eBay and those that are listed in the under $30 range are from China and those that are around $50-$70 are aftermarket from the States. The OEM Denso part is around $250. Do you think the after market ones are good enough? I like to stay away from buying from China.

My car has been pretty reliable up until 2017. Not sure if any of the below works on my car is related to the problem I am having now or not.
April, 2017 - Replaced head gasket. Luckily it was the outer gasket so coolant was leaking out and not into the engine.
June, 2017 - Replaced alternator

RXGS

iTrader: (2)

I rolled the dice on a used OEM MAF sensor as I wasn’t sure if it was my issue, but it ended up working perfectly.

As as far as previous repairs, the head gasket is kind of eye opening, but as to whether it’s contributing you your problem it’s too hard to say.