Can anyone elaborate (or even better post pictures) of how far in/out the screw should be set on the fast idle cam adjustment screw (on the firewall/oil filter side)?

Im having some idle funky-ness so suspecting that could be part of it.

Also.... from what i understand the JDM's dont have the AWS, so why the fast idle cam/adjustment screw?

Sorry if its a dumb question just not overly familiar with the fast idle cam setup and what it does/how it does it

Thanls

 

Let me talk about how the system works, and why it works, so that adjusting it makes sense. On any modern car today we have electronic throttles. There is a motor and some gears connected to a butterfly valve. The computer can open that throttle however it wants in cold and warm condition. There are no idle air control valves, throttle cables, cruise control actuators, any of that.

In the throttle cable era however you needed a bunch of different devices to accomplish what we can do with one integrated drive-by-wire system. In the case of an FD (and a lot of cars back then) you had a bunch of things contributing to the idle airflow.

1) the throttle plate and its adjustments
2) the air adjusting screw under the TB, basically a controlled air leak
3) a mechanical way of physically opening the throttle when the engine is cold. This is the thermowax and fast idle, something basically borrowed from carburetors.
4) an idle speed control valve, another controlled air leak commanded by the ECU
4) in the US, to force the catalytic converter to warm up we had the accelerated warm up system. That's another valve.

The fast idle cam physically opens the throttle plate. There is thermowax inside which expands when the engine warms up, in the same way a conventional thermostat expands to open a valve and let coolant move between a radiator and an engine. Those other systems are basically air leaks.

This is a USDM manifold but the principle applies.



now here's a diagram from the service manual. The cam rotates like the arrow indicates.



When the cam rotates away fully, the fast idle system will NOT open your throttle plates to raise your idle when the engine is cold. You should have the same TPS voltages (VTA1 & VTA2 if you have a Power FC Commander to conveniently view) as when the engine is warm.

When the cam is resting on the thermowax and the engine is cold, your throttle plates should be cracked open more, raising the idle and increasing TPS voltage.

So here's what you do (and I hope I didn't get tighten and loosen reversed here). When you tighten that screw, you are basically creating space and actually moving the fast idle cam away. It can lower your cold idle and you lose that warmup functionality.

When you loosen the screw, you are bringing the fast idle cam closer to the wax rod. This will help raise the idle when the engine is cold (up to a point). If it's screwed out too much, your idle will never fully come down when the engine warms up. You will be able to rotate the fast idle cam with your finger to drop the idle though.

What I would do is warm the engine up (at least 80C coolant) and shut it off. Loosen or tighten the screw so that the TPS voltages are just fully closed, so that the idle isn't high when the engine is warm.

Now you can see some of the advantages of electronic throttle. You never have to deal with this. It just works.

 

Nice explanation arghx. Thanks for the trouble.

 

Thats percfect arghx!! Thanks for the great explanation!!

Cam

 

You're welcome

 

There should be Lines on the cam blade


Heat the car up fully, set it to 0, then set the TPS voltage after you have fast idle at 0. I always set every thing back to "0" or what i like to call 0 every time, it only takes the smallest adjustment to to miss your perfect idle

 

Awesome!

Thanks for the help

Cam