My 87 190E 2.3 with 170M runs well but stinks like sulphur and gets around 16mpg of 91 octane. I just bought it and have no basis for comparison, but I suspect the mpg should be much better. My first suspect in a case like this would be the Oxygen sensor. I took a peek under the car and the O2 sensor in front of the cat looks crusty enough to be original. When I shopped for a new O2 sensor I found two types avaliable. One is at the cat and one is at the exhaust manifold. My question is - does this vehicle have two O2 sensors, or one or the other?

Thanks!