I have a 323 Protege, 2001. I want to adjust the idle in order to take advantage of the lowest fuel consumption. Has anyone done that before? I did before with a Nissan Pulsar '92 model and over 240,000 and I got under 5/100km. The car has over 210,000km and I would expect that would lower the rpm and fuel consumption. Could anyone explain what idle does? Thank you heaps!!

 

Idle keeps the engine running while the car is stopped. While it idles the car does 0 miles per gallon, or uses infinate L per 100 km.
The factory sets an idle speed that keeps the engine running reliably, around 750 rpm. The idle control motor will adjust it up when you use the air conditioner, put the automatic transmission in a gear, and if a big consumer of electricity that puts demand on the alternator.
Some vehicles don't have an idle adjustment screw (Ford), it's factory set and electronically controlled.
Some newer vehicles turn the engine off to save fuel and when you touch the accelerator it starts up again.

In carbureted engines there is also and idle air adjustment. This will lean out or enrich the fuel air mixture. Doing this wrong can cost you an engine.

There is also an idle air screw on the throttle body of fuel injected engines. I suggest not touching these as it may upset the whole electronic fuel metering. I will not touch mine. If something goes wrong I would not have the computer to correct things. This is probably the set up you have in your protege. If you want to try anything only try adjusting the idle speed screw right there where the throttle cable is attached. Keep track of the original position so you can reset it if you don't like the results.

 

Thank you for all this info. My Mazda is a 2001 model, manual transmission, and I am seeking information regarding how can I lower the fuel consumption from the carburettor tuning, although engine is using injection. I used to have an old car on carby and I changed the nozzles (from 0.9 to 0.7); that nearly saved me about 1.5 litres per each 100km. Can the fuel/air mixture be improved to a better fuel consumption? Could the nozzles be changed?

 

No, this is a brave new world for you. Now just about all the physical adjustment you make will be rendered ineffective because the computer will adjust the other way.

There are few things you can do to improve fuel mileage.
Keep the engine tuned up, take junk out of the vehicle to drop weight, keep the tires properly inflated, make sure the brakes don't drag, and most of all: drive with fuel saving in your mind.
The right kind of oil can make a difference:Motor Oil 101 - Bob is the Oil Guy