[DML] Re: End of life for idle ECU's

["David Teitelbaum" <jtrealty@xxxxxxxxxxx>]

I recently worked on a car for a nearby owner that had a
hiccup-hunting type problem. It would idle smooth and had a regular
repeating bump up and down in the idle. Rob Grady tried to smooth it
out but the owner didn't want to spend a lot of time (read money) on
it so Rob had to leave it alone. I figured I "knew better" and just
had to substitute a known good idle ECU and maybe a Lambda ECU. My
origional theory was some kind of interaction between the different
control loops. As pointed out the ECU's only communicate with each
other by their interactions on the motor itself. I figured they were
chasing each other's tails so-to-speak. Ater swapping the ECU's and
several other things that we could think of WITH NO EFFECT I had to
think of something else. I started looking for vacuum leaks. I found
the "O" ring to the cold start valve under the mixture unit was out
and the brass piece that holds it in was sliding around on the tube. I
got the brass piece and the "O" ring back correctly and although it
made a BIG   difference, it still hunted a little. I still suspect
multiple vacuum leaks under the intake manifold but we didn't have the
time to "go digging" in there. In any case the owner was happier with
the improvement. You would think a vacuum leak would cause a constant
effect, not a cyclical one but I have seen it with my own eyes. Anyway
there was nothing wrong with any of the ECU's. The moral here is you
HAVE to correct ALL vacuum leaks or the control systems cannot work
right. Vacuum leaks also have a cumulative affect ie, many small ones
add up, not cancel out. I have done several motors and when you do all
the seals, "O" rings, and gaskets you can have the idle very smooth.
For Elvis where he notices a sudden cahnge in the idle it could be as
the motor warms up and one of the warm-up systems which uses vacuum
goes on or off he has a vacuum leak which is causing that, not
anything with the idle ECU. Of course you HAVE to have a tuned up
motor with clean fuel injectors, good ignition wires and good compression.
David Teitelbaum
vin 10757


--- In dmcnews@xxxxxxxxxxxxxxx, doctorDHD@xxxx wrote:
> 
> Dave T or anybody else.  My idle is pretty darn solid when I 
disconnect the 
> wire going to the idle speed motor.  It hunts bady when  connected.
 Is this a 
> clue as to where the problem is?
>  
> D² & 6530
> 
> 
> [Non-text portions of this message have been removed]








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