Performance Mixture Adjustment/Oscillation damping
For my daily driver car, I found I could get better overall performance (as well as eliminate the mixture oscillation) by unplugging the lambda
sensor and re-adjusting the mixture screw to it's sweet spot. The lambda circuit is primarily an emissions reduction system and has marginal value for engine performance.
You can do a simple and reversible experiment to see how you like the behavior of the system with the lambda sensor removed and the mixture re-adjusted. You do this as follows:
Unplug your oxygen sensor and start up your car and let the engine warm up (it's best to do any tweaking with the engine warmed). The oxygen sensor can be unplugged where it enters the rear firewall on the driver's side. It is best reached through the driver's side rear wheel.
With a high impedance volt meter, measure the voltage between the oxygen sensor lead and ground. Record this value as this will be important for returning your car to the original setting later if you want to undo the tweaks.
Adjust the mixture screw (it's between the intake and the fuel distributor) using a 3mm allen wrench (I use a long "T" handle one for
this as the adjustment screw is a ways inside the hole) until the voltage reading on the oxygen sensor reads slightly over 0.7V (I found
that my car was the smoothest at about 0.72V -- I'm sure the precise values is not that important and you can experiment
with this a bit). It's important that you only take the reading when the hole for the adjustment screw is plugged since there is a huge vacuum leak with the hole unplugged resulting in incorrect mixture readings.
Turn the screw clockwise to make the mixture richer (and increase the voltage from the sensor) and counterclockwise to lean it out. A little
turn goes a long way and you won't need to turn the screw more than a quarter turn.
After you've found a good sweet spot that gives you a pretty smooth engine at idle, go take if for a ride to see how you like the difference in overall engine behavior.
If the engine RPM increases when you increase the mixture, this is typically a sign that you have a vacuum leak. The RPMs increase because
there is too much air entering the engine (due to the leak) and when the mixture is enriched, the additional fuel essentially becomes equivalent to opening the throttle a little.
After you are done experimenting, you can return the mixture to where it was originally at by once again reading the voltage on the oxygen sensor and adjusting the mixture until the voltage is back to where it was originally. Then connect the oxygen sensor to the contact leading to the lambda computer.
Enjoy experimenting with your car.
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