Re: Idle Speed ECU

["dcsj4465" <dcsj@xxxx>]

First of all why are you asking this Question? What are your symptoms?

Here is a recent senario that I just fixed on someone elses car.

Symptoms were:

Car would start Ok when cold. Then run rough for acouple minutes and 
clear up. Idle around 800-900 rpm. Once engine was hot it would idle 
around 1200 rpm. If the car was shut off for a minute it would not 
start without pressing on the gas pedal somewhat.

I doing the diagnosis. I had referenced a recent article in DCS 
magazine written by David Teitlebaum. THANKS DAVE!! Stating that if 
you unplug the Idle speed motor. while the engine is running it 
should DIE. needless to say when I tried that NOTHING happened. That 
puzzled me,But I went on checking other things out. Finally I decided 
to start swapping Components from my own car. First was the Idle 
ECU, Result was no Change. Next was the Idle speed Motor, Result BIG 
change every thing worked properly Idle was 775rpm and engine started 
normally just by turning the key as it should. I put the orig ISM 
back on to verify my findings. As expected all the old symptoms 
returned. AS a side note you could HEAR the motor buzzing as though 
it were working. I took it back off then did some comparing with my 
good unit. I found the rotor valve to be frozen. After I decided to 
replace it I opened the unit up and found that the upper end of the 
armiture shaft had severly rusted into the bearing. I worked with 
until it was loose using WD-40. I got it freed up enough that it 
would operate somewhat normally. I reinstalled it and everything 
seemed to be working fine for a short time. But ultimately it would 
start to become erradic as the lubrication evaporated with the engine 
heat. The New unit is installed now and everything runs as 
advertised. and Yes If you pull the plug off the ISM it will DIE! 


We also found that with the ISM not functioning that the Idle speed 
micro switch also operates the vacuum solinoid controlling vacuum to 
the distributor advance and will cause the the Idle to drop from the 
1200 rpm to about 800-900 rpm if it is depressed. making you think 
the idle speed system is working. when it isn't.

So the Moral to the story is Don't assume you have a faulty IDLE ECU 
just because you have a verying Idle Speeds

Hope this Helps somebody out.

Dennis 5180 GULLWNG 


-- In dmcnews@xxxxxxxxxxxxxxx, doctorDHD@xxxx wrote:
> Does anyone have the schematic for the idle speed ECU?
> 
> Do they fail in any particular modes?
> 
> Thanks
> 
> Dave
> 6530
> 
> 
> [Non-text portions of this message have been removed]