Hi all
Happy owner of a 2008 IS250 here. Had it two and a half years and it's been a joyous ownership experience so far compared to previous German cars. There's one issue I'm having and after a lot of research on here and some Googling, I think it may be carbon buildup related. I wondered if anyone had any thoughts?
For the last few months I've noticed that low speed running is getting rougher. If I'm cruising along at about 1200-1500 RPM the car will gently shake and hesitate. It feels like a misfire. In addition, if I've been driving at anything other than slow town speeds and then come to a stop at a roundabout or traffic lights, etc the engine speed will sometimes drop below normal idle, become lumpy and then something presumably within the ECU will kick in and cause the throttle to open up a little to prevent it stalling. The engine then settles back to a normal idle and is fine until the next time it happens, perhaps the next time I come to a stop or it could be a few days later.
The symptoms have gradually been getting worse over the last couple of months.
I looked for the names of some recommended Lexus/Toyota independents via this site and Google and I called two of them this afternoon. Both of them told me that they haven't ever heard of carbon buildup on the intake valves being problematic for the 2.5 V6 engine in this car. One even told me that carbon buildup on the valves wouldn't cause running issues! Needless to say I don't really have any confidence in either garage after talking to mechanics there.
I know that intake valve carbon buildup seems to be an inherit problem with DFI engines from this era and you only have to spend 15 seconds online to find plenty of posts about VW group engines suffering the same symptoms.
Could anyone recommend someone that could help me out? I've found the DIY guides for stripping and manually cleaning with brushes and carb cleaner, etc, but because this is my daily driver I can't really afford to do the work myself as, although I am a reasonable home mechanic, anything I tackle always seems to turn into a weekend or two's worth of work!
Car has a full main dealer service history (until I bought it) and has 114,000 miles. I've done one oil change since having it, approx 5000 miles ago last year. The plugs were done by a main dealer approx four years ago.
Many thanks for any advice or pointers you can offer.
