Hey my Man,

I believe that there is a screw that can adjust the air fuel mixture(or does it only adjust the idle speed), located in the body below the IAC motor. Is it true?

Don't ask me why. I am simply curious.

 

No, you are forbidden to answer, please delete your response at once.......

 

with no hard feelings, but I somehow trust TheMAN to give me the right answer.
The reason I amasking is that I reduced my idle speed by turning down the screw(clockwise) and this time around I get a mileage of @300 mile to the tankful. I never got more than 240 before.

 

Can anyone show me where this screw is exactly with a pic?

 

Wow...I can't believe no one is going for the "chikoo and theMAN" joke...Oh wait, I guess I just did.

Anyway, wouldn't turning the screw clockwise raise the idle, instead of lowering it? I thought those little setscrews usually "pushed" the throttle body further open when you screwed them in, unless this one's backwards somehow.

 

The throttle body isnt normally used to control idle speed (notice its fully closed when the engine is idleing) hence the need for a "Idle air bypass valve." By turning a screw on the IAB valve clockwise, you are closing an airpassage, thus reducing idle speed.

 

Ah. I see. I haven't really messed with one since my VW days, which DID use the TB to control the idle. (the old Bosch mechanical FI system)

 

Did you say you got 240 miles per tank before? Damn you must have a lead foot. I usually get 330 miles before my light comes on.

 

well I drive mostly city under 40mph with traffic lights every other mile.

 

Found this idle speed adjustment method over at another not so popular Mazda forum.
Can anybody verify if this is the right procedure?
(or wrong!!)

Check your base idle.
Turn off all electrical equipment.
Open the diagnostic connector and you'll see a diagram inside the cover. Connect the contact labelled "TEN" to the one labelled "Gnd" using a few inches of wires.
Start the engine and check the idle speed.
Adjust the screw in a metal cylinder sticking out of the top of the throttle body to get the idle to around 850-900 rpm.
Sometimes this screw has a rubber bung over the top of it.
Note that you cannot properly adjust the base idle without connecting Ten->Gnd.

 

OK, I don't know about Protege's per se, but on another car I own it is expressly stated that the idle adjustment screw is NOT to be messed around with, since it is set at the factory on the flow bench, and will never be right again once you moved it. It's there in case you HAVE to replace your t-body. That's particular to one of my cars maybe (1993 Saturn SL2) but I assume it prolly applies to all t-body MAP sensor cars. Again, I don't know, just something I thought I'd throw out there.

 

Wrong. This is the correct procedure for a pre-OBDII Miata, but it won't work on a new Protege.

99+ Proteges use a motorized idle-speed controller (IAC valve in official car-speak) that uses a conputer-controlled valve to automatically regulate the idle speed. The idle-speed screw will change the idle speed if things are way out of whack and the IAC valve can't correct the idle, but if the intake system is in good shape (i.e. no vacuum leaks, clean and properly adjusted t/b, etc.), the idle screw will do nothing because the IAC will automatically correct the idle back to what the PCM thinks it should be.

The car also has a throttle position screw below the t/b with a little cap on it. This screw is preset from the factory, and according to the FSM, it should NEVER be adjusted.

BTW there is no way to manually adjust the idle air/fuel mixture on a new Protege, or most other new cars. This is not 1980, and this is not Bosch L-Jetronic EFI. If your car is idling wrong, it has some sort of fuel or ignition problem and should be checked for codes.

 

Which is exactly why I don't mess with things like that...But sometimes I long for the good ol' Webers on my old Bug!

 

wouldn't 1980 be K-jetronic?
just messin' with ya

that screw is an air bleed adjustment. you should never have to mess with it.

 

I have to break this to you guys, but messing with it did cause some changes in my idle setting.

For one, after I pushed it down(reduced air flow), now the idle would droop when engine is cold and when I come to a stop.

Secondly the Auto transmission now shift smoother into 1st when coming to a stop, as compared to before when I had the screw wayyy up(too much air).

Also I used to get 240mile to the tank with the air bleed screw wayy up.
After pushing it downnnn, i got a more satisfactory 300 miles to the tankful.

So there definitely is something there.
What? how?

btw, after turning the scew, i used to disconnect and reconnect the -ve terminal of the battery.