Well, continuing in the never ending saga of my 190E the latest thing that I have to address is that the engine idles rough and I seem to be using more gasoline than I should (of course I can't be positive about that because the odometer is broken, but I will save that for another thread). The manifold vacuum indicator seems to be reading higher also. I put sea foam in the gas tank but this made the problem worse. I was told that inasmuch as the car had sat for a long period of time that the sea foam was actually dislodging contaminents from the gas tank and plugging up the fuel filter......but I have changed the filter. I was also told that the car has two filters, but I can only find one........next to the fuel pump and the fuel accumulator (whatever the hell that thing does??). Any ideas?
Poor mileage, rough idle . . . check the O2 sensor and the connections from the sensor to the CIS; check the other sensors that provide the CIS with info, like the temp sensor for the intake and other parts of the system. Hopefully, to rule out the cheap stuff first.
Thanks MTI (yet again) How does one "check" the O2 sensor? Does one need a special tool?
How do I test my sensor?
Using a digital voltmeter with reasonably high impedence (20K ohms or so), you can measure the voltage output of your O2 sensor while it's connected to the computer, with the car warm and running of course. Just find the single wire connector coming from the sensor that goes to the computer - not the one that has two wires, that's the preheater on some sensors. Set your meter to a range near 1 volt - the sensor's output falls in the 0-1 volt range. Ground the (-) probe to the head or the battery, and clip the (+) lead to the sensor output. You should be getting a reading in the neighborhood of 0.45 volts, fluctuating a bit up and down. If you get no voltage or a low voltage, your sensor needs replacement.
The life of an O2 sensor varies depending on fouling, vibration, but Mercedes estimated it to be somewhere under 100K miles. As a result, they built in a signal light that got tripped by the odometer at approximately 60-90K miles that set off a dash light. In early model W201s, the "reset" of the dash light was accomplished by removing the bulb from the socket. Later, around 1987, they changed it so that you could reset the light via a button located under the passenger seat carpet near where the cable from the sensor enters the cabin. If it is the sensor, remember that the Bosch sensor for a V-8 5.0L Mustang is the same part with a different wire harness, but a lot cheaper!
Linear Mode
