Idle adjust screw

[joyluck614]

Dear Sir:

900 to 1000 rpm is around normal for a 12R at FAST IDLE - when the A/C is ON.

When the A/C is OFF the idle speed should be around 700 to 800 rpm. That will help a lot with fuel economy AND make it easier for you to shift in traffic.

Your carburetor should have an FAST IDLE system - this is usually a solenoid-switched, vacuum-actuated diaphragm that pulls the throttle to a higher setting (higher rpm) for powering accessory loads like the air conditioner.

Note: this system is different from the one you previously adjusted the CURB IDLE with. It has it's own adjustment screw.

To look for the system, first set your curb idle to 700 to 800 rpm - like you did before. The CURB IDLE screw is always very close to the carburetor body and farther away from the throttle linkage.

Then with the air cleaner assembly removed, and the carburetor throttle linkage exposed to your view, have someone inside the car turn on the air conditioner.

You should notice the 'click' of the solenoid and some movement around the carburetor's throttle linkage system.

Look for a vacuum diaphragm that pulls the throttle shaft to a higher setting - you can't miss it if you know what you are looking for.

That's the FAST IDLE SYSTEM.

There should be a screw ON THE LINKAGE that allows you to adjust how fast the engine runs when the system activates - it is somewhere there among the throttle stuff. This screw is farther away from the carb body.

When you think you have found it, try adjusting it and see if the idle speed changes ONLY when the A/C is ON.

When you have found it, adjust it to 900 to 1000 rpm.

That way the engine will only speed up when the A/C is ON.

Hope this helps.

Dusky Lim

Dear Dusky,

what do you mean above about being easier to shift in traffic, pag mataas ba idle mahirap mag shift? ty

[joyluck614]

Oh one more thing, i just got my aircon repaired so i had to set my idle at 1100 para nasa 800 pag naka on ac, pansin ko lang ayaw pumasok sa gears nung paalis na ako, un feeling eh parang pag try mo isaksak sa 5th gear pero wala naman 5th gear, un ganon, related kaya ito sa pag set ko ng idle sa 1100? ty!!

[duskylim]

Dear joyluck:

The difficulty you are experiencing in shifting into gear is EXACTLY what I was talking about.

When the engine's curb idle speed is TOO HIGH, the synchronizers in a manual transmission will have a harder time equalizing the input vs output shaft speeds, resulting in the harder, more difficult shift.

When you step on the clutch, the release bearing is forced onto the diaphragm spring of the pressure plate, releasing the clutch disk from the flywheel, thereby dis-engaging the transmission from the engine.

This allows you to change gears, pushing on the gear lever does several things sequentially very quickly:

1) after selecting the desired gear and bringing the shift lever into the correct position, the 1st part of the push/pull forces the cone clutches together

2) the cone clutches are responsible for equalizing the speed of the input and output shafts

3) when the 2 shafts start turning at the same speed a toothed ring - called the synchronizer - slots into place, allowing -

4) a locking sleeve (called the 'dog sleeve') to slide and lock the two shafts together.

That's how a gear is selected and changed.

No doubt you've experienced a grinding noise and feel during a bad shift.

That's not caused by the transmission's gears themselves (which are always engaged) but by the synchronizer and dog sleeve refusing to engage and lock.

No when a transmission gets older and worn, those parts get a little loose, making it more sensitive to things like engine idle speed.

Keeping your idle speed low makes it easier to shift.

Best Regards,

Dusky Lim

[joyluck614]

Thanks once again Dusky, i lowered my idle speed down to 950 so when ac kicks in its around 700-750, comfortable enough not to make my engine vibrate. Havent had a hard time shifting since then

[theshepherd]

Why is mine the exact opposite? When my AC turns on my idle doesn't go down. Shoots up to 1000? That would be fine right?

[duskylim]

Dear sheperd:

The reason your idle speed goes up is because the FAST IDLE system (aka Idle Up system) is working correctly.

As I said BEFORE - the carb has a device used to raise the idle speed when it is necessary to drive accessory loads like the A/C.

In the case of joyluck he lowered his FAST IDLE speed to make it easier to shift.

Generally the Fast Idle system brings the engine RPM to around 900 to 1000 rpm - UNLOADED, but the load of the A/C will lower that speed to around 800 to 900 rpm.

If your fast idle speed is 1000+ rpm with the A/C ON, that's a little too high and will make your shifting more difficult and consume more gas.

The upside is that your A/C will cool very quickly.

Note: Please read the previous posts so we don't have to keep repeating ourselves.

Thank you.

[theshepherd]

Dear sheperd:

The reason your idle speed goes up is because the FAST IDLE system (aka Idle Up system) is working correctly.

As I said BEFORE - the carb has a device used to raise the idle speed when it is necessary to drive accessory loads like the A/C.

In the case of joyluck he lowered his FAST IDLE speed to make it easier to shift.

Generally the Fast Idle system brings the engine RPM to around 900 to 1000 rpm - UNLOADED, but the load of the A/C will lower that speed to around 800 to 900 rpm.

If your fast idle speed is 1000+ rpm with the A/C ON, that's a little too high and will make your shifting more difficult and consume more gas.

The upside is that your A/C will cool very quickly.

Note: Please read the previous posts so we don't have to keep repeating ourselves.

Thank you.

Thanks for making that clear. Looks like I need to adjust the fast idle speed again.
Another thing. Sir Dusky,
Which creates poorer FC, exhaust pipe with smaller inside diameter than stock or exhaust pipe with larger inside diameter than stock? And also why? I just need to know the effects.
Thanks again!

[joyluck614]

Thank you for all the advice Dusky

If you under-size your exhaust system over stock, it would be like fitting a smaller engine to your vehicle, SAKAL - indeed too much restriction and back-pressure and you will end up with WORSE fuel economy and power.

The same thing will happen (only MUCH, MUCH WORSE for fuel economy and power at the low and mid range) if you OVER-SIZE you exhaust system.

Siguro kung talagang barat ka sa gas, undersizing the pipes and mufflers by 1/4th inch will result in better fuel economy at the expense of top end.

^ i believe he answered it already

[belle17]

Thanks for making that clear. Looks like I need to adjust the fast idle speed again.
Another thing. Sir Dusky,
Which creates poorer FC, exhaust pipe with smaller inside diameter than stock or exhaust pipe with larger inside diameter than stock? And also why? I just need to know the effects.
Thanks again!

Sir Dusky,

Would you happen to know where is the adjustment for a corolla 16v GLI 4afe engine? My car will not compensate for the extra load of the AC. When I am not using AC the idle is on 1,000 RPM when I use AC it goes down to half and the engine is choking, and i have to rev up the enginge to give it a boost. Thanks in advance.

[duskylim]

Sir Dusky,

Would you happen to know where is the adjustment for a corolla 16v GLI 4afe engine? My car will not compensate for the extra load of the AC. When I am not using AC the idle is on 1,000 RPM when I use AC it goes down to half and the engine is choking, and i have to rev up the enginge to give it a boost. Thanks in advance.

Dear belle:

Isn't the GLi series of Toyota Corolla FUEL-INJECTED?

If so, you cannot adjust the idle settings without knowing how to set electronic fuel injection systems.

As most fuel injection systems are electronically (computer) controlled with various sensors built into the engine, you need to have the diagnostic system (test computer system) to adjust it correctly.

You will have to bring your car to an injection specialist or sa casa.

If I'm wrong and your Corolla is carbureted, then go back to the old posts of this thread, the same advice I gave before applies to you.

Sincerely,

Dusky Lim