W210 Mass Air Sensor & Check Engine Light

use a vacuum gauge of course

I use a stethoscope, but Dealers use a Smoke machine. If you do the 02 sens tes tand do not have a lean [ low v] reading , you do not have a vac leak. The important check first is the fuel regulator ..which causes both a rich condition and a vac leak at the same time Email me ...

AJ, i think i should send a diagram to JACK so that he will know where the fuel pressure regulator is!

That would be cool.. I did point it out , but a pic is much better... Be a shame to change out the $400 MAF for the sake of a bad regulator.. ..I won't even touch a fuel trim code diagnosis til taking a FP test... seen it too many times....

yeah man

CSC/AJ -

I checked the vacuum and it was steady at 20"hg even when I wiggled all the tubes & ducts I could find. My car is a V-6 (1998 North American model) - there seems to be a vacuum switch that then branches to TWO "regulators"? I measured the vacuum at points A & B of what seems to be a vacuum switch - It was always about 20" at A. At B it was 19" during warm up and then dropped to zero.

See pictures at

I checked the resistance of the MAF - It was 4060 ohms at 8C which is a bit high (should be 3420 to 3780 at 10C or 2299 to 2541 at 20C). Voltage to MAF was also in range 5.02V. (should be 4.7-5.3v) (from Star Tek )

I tried to find the O2 sensor connection under the passenger side carpet - even removed the plate in the footwell under the mat, but could not find the green wire. Just two large bundles of wires passing through with no connectors. Maybe you were thinking of the earlier W210?

Since I cleaned the MAF, the CE light has not come back on, but I have not driven very much. One thing I wondered, is if the relay that actuates the MAF cleaning cycle might be faulty - but I have no clue how to check this.