Re: Fw: RE: Dak doesn't want to stay running

From: jon@dakota-truck.net
Date: Sun Nov 20 2005 - 22:40:36 EST


"Jay & Dana" <jay&dana@telus.net> wrote:

: This is my second posting and I would still like to know about this ISS
: screw. As I mentioned before I didn't think we could adjust the idle speeds
: in our Daks. It was also earlier mentioned that the people posting on the
: DML has dropped. Maybe it's because when people ask questions, they get no
: response.(except for salt on the roads and winter beaters.) Damn, I miss
: Bernd :-)

   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 --'



This archive was generated by hypermail 2b29 : Thu Dec 01 2005 - 10:10:44 EST