mpolli

Based on the age of the car, I'm tempted to agree with you but, it bothers me that he does'nt have the Check Engine light on.
Possibly the catalytic converter " going south "?

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2007 C 230 Sport.

Could be. However, often the O2 sensor failure is not detected by the computer. It can get sluggish. As far as a shotgun approach it is cheaper to try than the cat. Also I think it is more likely. Most cats are replaced because they rattle apart as far as I know. As long as the O2 sensor is fairly cheap I would throw one in. The Bosch ones are kind of spendy but the universal ones are 30.00-45.00. But I don't know how you pick a universal one since I have seen 1 wire, 2 wire, 3 wire and 4 wire... Maybe he could get the O2 sensor tested for a reasonable price?

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra