Thank you Jon!
I love reading your responses becauses they are almost like reading a short
novel :-)
I think I will just leave it be, as I don't want to "screw" anything up.
-Jay
> Jay,
>
> If you are standing in front of the engine bay looking at your
> throttle body, on the left side you may see a set screw. They come
> blocked off from the factory though, so if you just see a metal cover,
> you will need to jam a screwdriver or something in there to remove that
> cover in order to be able to access the set screw. If you go around to
> the passenger side of the engine bay and look at the throttle body,
> you will see that the throttle linkage rests against a screw. (Move
> the linkage by hand and you will be able to see where the screw is
> stopping it.) That screw is the other end of the set screw I mentioned
> earlier. After you remove the metal cover to be able to access that
> screw, you can turn it clockwise to "increase the idle" and of course
> counter-clockwise to "decrease the idle".
>
> I put "increase/decrease the idle" in quotes because this is actually
> not what this screw is for. Turning the screw merely adjusts the position
> of the butterfly valve in the throttle body. It is the IAC (Idle Air
> Control) motor which actually controls the idle - this is the plunger
> at the very back of the throttle body (closest to the firewall). The
> computer monitors the idle RPMs and adjusts the plunger of the IAC to
> achieve its desired idle. Lets say you want to increase your idle -
> if you turn that screw in, the butterfly valves will open, the idle
> will increase, the computer will notice that it is increasing, and it
> will close the IAC to compensate. Eventually, you will be able to turn
> the set screw in far enough so that the IAC is completely closed and
> the computer is no longer able to compensate. Unfortunately, at this
> point the computer assumes you have a giant vacuum leak and chances are
> pretty good its going to complain. The opposite scenario is true if
> you are trying to use the set screw to decrease the idle - the computer
> will compensate by opening up the IAC. However, when going in this
> direction, the truck is capable of idling with the sole intake of air
> being via the IAC, so even if you back the screw out all the way, you
> won't be able to decrease the idle. Also, what will happen is that the
> "stop" for the butterfly valve will no longer be the set screw, but the
> blades of the valve itself hitting the throttle body bore. This results
> in undesireable stress on the blades and could potentially cause little
> bits of aluminum to be ground out of the bores of the throttle body and
> ingested into the engine.
>
> So I guess what it comes down to is, the "proper" way to increase
> the idle is to do it via the computer, either with some sort of electronic
> trickery to make the computer think the idle is different than where
> it actually is, or I suspect a dealership's service department could
> probably flash your computer to increase the idle. You can give
> the set screw method a try if you like; if you only want to bump the
> idle up a little bit, perhaps it will be within the acceptable margin of
> error for the computer, but if you keep screwing it in and the idle
> isn't changing, then the computer pukes codes at you, at least you
> know what happened. :-) Doesn't hurt to give it a try, but you'll
> probably want to count the number of rotations you move the set screw,
> so that you can put it back to where it was originally, if need be.
>
> If you haven't reset the computer or changed your battery in a while,
> you might want to give that a try also. I know when I was regularly drag
> racing my '96 Dakota, for consistancy I would always reset the computer
> before every run so tht it wouldn't have a chance to learn and change
> anything on the next run. After the last run, I'd just leave it alone, so
> from the computer's perspective, it "wakes up", connected to an engine
> that it hasn't learned anything about yet, it idles to the starting
> line then gets hammered for 1/4mi, and idles back to the pits. Sometimes
> when coming home from the track, the truck would idle around 450-500rpm.
> I'm not sure what it was about that which made the computer want to
> idle low, but anyway - if it is idling too low for you, resetting the
> computer is certainly an easy thing to do. (Disconnect the negative
> battery cable and then put the key in the ignition and hold it on "start"
> for about 5 seconds. If you want to leave it disconnected for 5 mins or
> so afterwards just to be sure any residual voltage has left the PCM, that
> wouldn't hurt either.) Sounds like your truck has always idled too low
> for
> you, so chances are this won't help, but like I said, its easy to do
> and the only downside is having to reset your clock and radio presets.
>
> Good luck with it!
>
> --
> -Jon-
>
> .-- Jon Steiger ---- jon@dakota-truck.net or jon@jonsteiger.com --.
> | 67 Coronet, 70 Cuda, 90 Dakota 'vert, 92 Ram 4x4, 96 Dakota |
> | 96 Intruder 1400, 96 Kolb FireFly, 99 Cherokee, 01 Ram 3500 CTD |
> `------------------------------------ http://www.jonsteiger.com --'
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