I have a '94 LeBaron sedan 3.0. I have noticed lately that there is excess carbon in the exhaust after the engine idles for five or more minutes. The exhaust is light grey and smells foul. It does not have any blue in it. Any ideas? This is not oil burning, I know my car does not burn any oil. The engine runs very smooth, and this carbon exhaust disappears during normal driving. It's only when she idles for a long period of time. She has 117K on her with the original O2 sensor in her.