Eduardo Santos

Hello everybody.
1987 Mazda RX-7 FC S4 N/A
A few days ago, I was trying to adjust the idle speed (because my car's idle speed is somewhat high, about 1100 rpm), and was going through the procedures described in the FSM, although I don't have some of the equipment they refer there such as the tachometer.

Anyway, I attempted at adjusting the idle speed and I tried to turn the air adjust screw clockwise, but couldn't because it was already fully turned. So I turned it counter-clockwise but instead of lowering the idle speed, it raised it...

So my question is (because the FSM doesn't say so): when the air adjust screw is turned clockwise does that make the mixture richer or leaner?

AGreen

iTrader: (11)

That doesn't adjust the mixture, that allows air to bypass the throttle body, thus making it idle higher or lower. If you're experiencing a high idle, I'd check for vacuum leaks first.

lastphaseofthis

iTrader: (8)

with the engine idling, spray starter fluid around and on hose ends, and connectors, anywhere air might leak, don't be stuipd with the starter fluid around the exhaust, i would actually only do this cold and freshly cranked..... and have a fire diminisher.

Eduardo Santos

Ok, thank you guys. I'll try that and see if I find any vacuum leak.

About the air adjust screw: when you say that it makes the air bypass the throttle body, that means it doesn't go onto the intake system?
And when it's fully turned clockwise does that mean, that the air bypass is at it's minimum or at it's maximum?

HAILERS2

Anti clockwise lets less air in. Clockwise does the opposite of that.

Early 87 have a variable resistor that has a screw. That screw only turns approx 3/4 or a turn then it hits a stop. Turn that screw clockwise and the mixture gets richer. You can guess what happens if turned anti clockwise.

AGreen

iTrader: (11)

Think of it this way. The gas pedal isn't really a "gas" pedal, it's an air pedal. It controls the throttle body, which controls the amount of air entering the engine. The computer figures out how much fuel to inject, based on things like throttle position, manifold vacuum, rpm, air flow, etc. So there's a passage that goes between the front and rear of the throttle body that has a screw smack in the middle of it. When the screw is fully shut, it blocks off the passage. When you turn the screw counter-clockwise, it allows more air to bypass the throttle body, thus causing the engine idle speed to increase. That little screw does the same job as the throttle plates, but on a much smaller scale, making it easier to control idle speed. That screw should be set so that when the engine is running at normal temperature, with NO loads on (AC, headlights, radio, etc) it should be right at 750 rpm. Then, if any other loads kick on that will tend to try and drop the idle speed, the BAC will open up, doing pretty much the same job as the adjusting screw, it automatically bypasses MORE air to the intake manifold to further increase the idle speed.

Eduardo Santos

That was a good explanation, I understood you
Although I though that the fuel to be injected was only calculated by the computer on the S5 model. Because mine is a S4, I thought it was different.


Are you sure?


Yep, mine has one of those... I may adjust that one, because petrol here in my country has more octane than petrol there in the USA (my car was imported from the USA).

soulrider

iTrader: (1)

I'm having an idle problem now. When I start it up, it stays at 3000 rpm alll day.
Just to make sure, this is most likely a vac leak right?

Eduardo Santos

It can be, but that's not the only thing that can cause it. Does it also happen if you start the car in gear and with the clutch all the way in?

satch

iTrader: (1)

Disconnect the plug to the BAC when this is occuring and see if it lowers the idle. If it does not then w/the plug disconnected and the engine off place a ground to one of the BAC pins and 12 volts to the other pin ( the pins are part of the BAC itself and not found in the disconnected plug) and you should hear a click each time that voltage is placed against one pin and a ground to the other pin (and make sure as to not place both the voltage and ground to the same pin by accident). Also measure the voltage on both wires to the Air Bypass solenoid w/the engine running but after 20 seconds of the engine running at 3000 rpm. The wire colors at this solenoid are Black/White and a Brown/Yellow wire.