300E running too rich for CA smog test, CO too high

Alex, here is what you need to do. Tell us what year your car is.

But assuming it's pre '92 from you describing it as a 300E:

take cover off X11 on your left front wheel well. put a scope on pin#3 and pin#2 and look at the duty cycle. Put an appropriate (forgot the exact size offhand) allen key down the open hole in your air filter housing and turn the screw 'slightly' clockwise (I think that's the right direction, but you will see the changes in duty cycle on your scope) you probably should not go below about 40% or thereabouts. You could use a voltmeter, but it might be difficult since the voltage might jump around a fair bit making it difficult to estimate what your duty cycle is... on the scope you can see this nicely even though it jumps around since you are simply looking at a 10 ms (100Hz) square wave If this is all gobbilty gook to you.... take it to your dealer.

cheers, guenter

Change the oil and all filters.

Add some gas line antifreeze and use premium. Take the car to be tested HOT after it's used up the tank of fuel with the gas line anti freeze.

New plugs wouldn't hurt either.