Check Vsc, Check Engine Light On 06 Gs300

[Austin GS]

Bought a used 2006 GS300 about 4 months ago. After about 1 month, the check engine light came on in addition to the Check VSC message. Took it to the Lexus dealer, and they replaced the gas cap (multiple posts in this forum about the gas cap issue). After a week or so, check engine/VSC came back on. After a second visit to the dealer, they suggested that I had bad gas. This sounded ridiculous since I always fill up with 93 octane Exxon. Anyway, went through two tanks of gas, and still getting the check engine/VSC. I'm always careful to screw the new cap down to at least 2 clicks on every fill up. Finally broke down and bought an OBDII tool to check the codes, and it showed P0300 (random cylinder misfires and multiple other P030x codes (misfires on all cylinders). After resetting the codes, I have noticed/felt misfires on cold starts, followed by the check engine/VSC coming on. Also seems like my fuel economy is lower than normal (averaging about 18.3 mpg in mixed city/hwy use), and also have carbon buildup on tailpipes (running rich?). Have replaced the spark plugs and battery, but check engine/VSC lights keep coming on. Had a local shop test for a vacuum leak, but they didn't find anything. Seems like any issues with the MAF sensor, O2 sensor(s), or other air/fuel delivery systems would trigger other codes. Any ideas?

[Austin GS]

No ideas, huh? I've taken it to the dealer twice in addition to another shop. No one can figure out what's going on. It's intermittent, so very difficult to troubleshoot. On average, the misfires happen about twice/month. Always on cold start. I have been resetting the codes myself when the misfires happen, and the car runs fine.

[Mr.Lexus3475]

I have the exact same problem all the way down to the black tail pipe, the dealer was no help. I did notice that it happens more with extreme cold or heated days...always on a cold start. After driving for at least 5mins and you turn off and on the car ... the light will then go off. When the light is on traction control doesn't work and I believe ABS doesn't work as well(no sure on the ABS as I haven't tested it, I know traction for sure).

My car is the 06 RWD GS300 as well.

Any help anyone can provide will greatly be appreciated.

[spine911]

I have the exact same problem all the way down to the black tail pipe, the dealer was no help. I did notice that it happens more with extreme cold or heated days...always on a cold start. After driving for at least 5mins and you turn off and on the car ... the light will then go off. When the light is on traction control doesn't work and I believe ABS doesn't work as well(no sure on the ABS as I haven't tested it, I know traction for sure).

My car is the 06 RWD GS300 as well.

Any help anyone can provide will greatly be appreciated.

This is a DEFINITE Carbon Buildup issue.

Ask/demand dealer to start a TAS case (Technical Assistance System) on your vehicle.

I strongly advise you to call Lexus Corporate---Lexus is aware of such carbon buildup issues.