As some of you are aware of the carbon build-up becoming prominent on IS250's, I've decided to use this thread as the sum of driver experiences with this issue and as an open discussion on how this issue is being addressed.

If your vehicle is experiencing any of the following symptoms, then it's most likely cause is carbon build-up;

- Rough idle
- Surging RPMS at stop light
- Low idle with vehicle shaking as if it was about to stall
- Cylinder misfire codes

As you browse through the discussion you will read rare cases of this issue not being solved.

Formally Lexus has addressed this by issuing the following service bulletin:

L-SB-0029-10 MIL "ON" DTC P030# and/or Intermittently Runs Rough

Please note that on several cases the exhaust valves were to blame for causing some idle issues.

UPDATE: I have had the dealership perform the latest service bulletin LSB, as far as its effectiveness goes, it took care of the issue. It's now been several months and 10,000 miles later and I have only had the car surge once but never again. Also I have not done an oil change since they performed this service so it's still on what ever oil the Lexus dealership used. That will change as of this week, but in essence I can say that the rough idle and the surging at stoplights has seized. Vibration has also notably gone down from what it used to be when the car was at a full stop in a stop light. I will update the progression as time goes. If you have had this service done please share your experience in terms of fixing most of the issues that are present.

 

Usually a new thread has something in it, just putting that out there...

 

this thread does not deliver.....yet?


at least give us something instead of a blank post.

 

dont baby your car. give it WOT from time to time.

 

^ i'm down with that. Its a sport sedan after all

 

I mean, I baby my car, but not in a granny way! I go WOT maybe 3 times a week...more than enough. There is something causing this, and I believe its the way the gas is burned ...most likely emissions related. Remember, direct injection is a cousin of the diesel engine...and is notorious for its "truck like" characteristics. I'm wondering if the carbon build-up is one of those characteristics that we just have to live with??? Sucks!

 

I'm not sure. I rarely notice the rough idle, usually on start up and within the first mile do I notice it. Quite frankly it seems to more likely occur (or at least in my case) when it's cold out. I've tried to give it a little rev (not necessarily WOT) and it fixes itself usually.

Come to think of it, I don't baby my car, I usually give it a WOT run 4-5 times a week for about 5-10 minutes before heading home and on the weeks that I don't, it occurs more often. Don't know if this helps you guys at all.

 

a question, for those who go WOT once in a while to minimize carbon build up. Do you mean, for instance, when getting on the highway go WOT till you reach the speed limit? That's what i thought at first, but then i read what kuuqi said, perhaps i misunderstood the concept?

 

i tend to WOT up to speed limit late at night when nobody is around from time to time, i love being thrown back into my seat

 

I've gotten the rough idle maybe 5 times in the 2 years I've owned my car. It usually happens after exiting the freeway and waiting at a stop light. I'll try to WOT more, and I've been dropping the Chevron fuel injector cleaner into my tank from time to time.

 

I second this. This is usually when mine happens too. Off the highway, stopped at a light or off ramp. Almost seems like the car is about to stall. Only does it for a bit and then goes back to normal. Doesn't happen when I'm actually driving or anything, only at idle.

I probably go WOT 4-5 times a week as well.

 

I really don't think carbon buildup has anything to do with this. I reset the computer in my car by disconnecting the battery, waiting a while and reconnecting. I immediately noticed better control of the idle.

Instructions to try this yourself:

1) Drive car to full operating temperature. You want to evaluate the difference resetting the computer makes on the response, so you want to leave everything else constant - such as engine temp. Pay attention to any idle vibration you feel in gear.
2) Power off, and remove the negative battery cable (10mm socket required). Leave off for 10 minutes or so. I discharged the system completely by pressing the brake pedal.
3) Reconnect negative battery cable
4) Restart and drive.

As I said I noticed better idle control and smooth idling. It may go back to what it was -- with more engine vibration through the steering wheel if the computer parameters change -- but I believe this result shows that there is nothing physically / mechanically wrong with the engine because the only thing that has changed is the fuel trim in the computer. I bet a software update at some point fixes this.

Finally, as for carbon -- I think there is no way the engine can be so carboned up by 15 - 20k miles that combustion or movement of the throttle plate is impaired.

 

Good info coming up.!

 

I am going to re-open this thread but some information needs to be posted by the weekend relative to the topic.

We also do not "save" spots unless you are a part of the moderator/editorial team.

Thanks.

 

I hope this does not become a wide spread problem....