Back when I first got my spec B's in, I was very disappointed with the idle shutting off at every stoplight...

Using only a vafc and turning that screw on the throttle body ccw enabled me to steady the idle. I wasn't exactly sure what the screw did, but it seemed that when i let off the throttle (after it having a load), the rpm drop wouldn't drop below the normal (~800) idle point. The more you turn ccw, the less the rpm will drop when you immediately get off the gas. If you adjust it perfectly, the rpms will drop to 800 and then stay there at idle. This is of course affected to some degree by the temperature, humidity, barometric pressure, altitude, etc.....

But what EXACTLY does that idle screw do? I mean, I know the effects but how does the ECU compensate? By measuring air flow at idle and adding MORE or LESS fuel according to the base maps?

.....And since I'm letting in so much MORE air in at idle with the spec b's, the stock maps can't compensate enough so the car would die?

Fast forward a little bit to when I had toda header and ran open header to the tune of anywhere between -35% and -45% at 1k rpms. I made good low end and good high end, and had a rock solid idle by "tuning" the idle by playing with the throttle screw and vafc leaning.

Now that brings us to present day:

The toda header has been replaced by hytech header and I've also installed a 9lb flywheel, and I'm playing with the open header idle... -50% (Max you can take out fuel with the vafc), and 5+ full turns of the idle screw and sometimes the car will still shut off. I'm fabbing up a cutout and it should be done this week, but if I want to run open header at the track I'd like to tune it for that...

So can someone give me an explanation? How far is too far on the throttle screw? And is the header THAT much more efficient or flows better, or something? Or is the lighter flywheel making the rpm drop too much easier and it just drops too much?

 

That screw determines the amount of air that is bypassed through the IACV valve. It's not electrical, just mechanical.

 

I would suggest you also try adjusting the throttlestop.

 

Why are they saying never to touch that in the Shop Manual?

 

They say a lot of things in the shop manual.

I would think they say that because the TPS is set from the factory with
break off bolts. When you move the throttle stop you have to recalibrate
the TPS afterwards.

 

The ECU doesn't measure air flow, it mainly measures manifold pressure, Air temp and throttle position. Air flow's not even a part of the Honda engine equation.

 

If you are adjusting your idle with the IAC screw, you are going about it the wrong way.

Unless you've modified the TB or the IACV, the screw should not be touched.

 

Oh well, too late now.

Suggestions?


[Modified by Black R, 1:52 PM 5/14/2002]

 

Reset it using the factory procedure:

1)Check timing
2)Pull IACV plug
3)Adjust bleed screw until idle is approx 450rpm
4)Plug IACV back in

If you have an adjustable TPS and you mess with the throttle plate you want to reset the TPS to read .5 volts when the flapper is closed. The voltage comes from the red/green wire.

A good idle is a function of the timing, IACV bleed screw, throttle plate screw, and TPS voltage.

 

450? I dunno about you, but my car shuts off under ~600 rpms... Unless you mean indicated on the stock tach - which is off a little... I'll double check the helms, but I'm pretty sure stock should be 800 +/- 50

 

I had the exact same problem with my B's. The problem with these cams is that they don't create a lot of vacuum.

Adjusting the TPS helped me - but I still find the idle a little lumpy until the car warms up (oooh yeah). In addition to a light weight FW, I have lightweight pistons, rods and a lightened crank - so my rotating assembly is much lighter and had a tendency to stall when the rings were still new and tight.

I think most Toda B's need to be leaned out significantly at idle - more than a V-AFC ("voltage adjuster")can compensate for. More reason to run a Hondata setup.

Try the methods listed above for adjusting the IACV - it should help too

 

VAFC will lean the mixture out plenty, uless your running 1100 injectors and 89psi of rail pressure.

Since there is less vacum the ECU pours more fuel in but there is no throttle (air) to use up the extra fuel thus, stalling occurs.

 

What Yack said. I was able to lean enough with the V-AFC to keep mine running at all times. Changed with the seasons, as well. Cold weather - different fuel at idle than hot weather.

Also, keep an accessory on would help keep it alive - either lights, blower on 1 or both.