What's really disappointing  is seeing how VW realized this overheating
problem in the ECU, and went back to the original design,  (with
the ignition module removed)  in the 88-92 digifant  golf/Jetta.

                                                              Joe  W.

Ken Wilford wrote:

> I had a customers van here not too long ago with idling issues.  Of
> course you need to check your grounds and the throttle position switch
> first to see if these could be bad or out of adjustment.  If they are
> fine then I usually swap over the idle computer from a good running
> van.  If that doesn't work I swap over the valve on top of the engine.
> Still bad?  I was scratching my head on this one, then I just tried
> swapping over the engine ECU.  Idle went back to normal.  Apparently
> something in the Engine Control Unit itself (under the back seat) was
> causing the idle problem.  Just an idea.  I have all of these parts to
> swap around so it makes it easier for me to test for these problems.
> You could try swapping in an ECU from a good running van from 86-91
> (they will all work) and see what happens.  I have rebuilt units with a
> one year warranty for $250 if you find you need one.
>
> Just FYI:  The factory 2.1l ECUs had problems with three things.  They
> decided to integrate the ignition module into the ECU so it got hotter
> than the older ones with the separate ICM.  Then they stuck it under the
> rear seat where it gets no air flow.  Then who ever was building the
> boards decided to do a crappy solder job on several of the connections
> (cold solder joints).  Murphy's law was in full effect that day!
>
> Hope this helps,
> Ken Wilford
> John 3:16
> www.vanagain.com
>
> Tabe Johnson wrote:
>
>> To recap:  Both my engine and that of Larry Himli (both 2.1s)
>> idle around 2400-3000 rpm.  In my case, it used to be that it
>> would just do that till it got warm, then it would idle properly,
>> and sometimes pop up to idle at 2400-3000 rpm.  Now it does
>> it all the time.  I swapped out the idle computer.  No change.
>> My temporary  fix: Unplug the idle air bypass solenoid.  Engine
>> runs great otherwise.
>>
>>
>> Larry's AC thing is interesting -- it says that the idle computer
>> is at least trying...  I'm still wondering about the
>> computer.  There was a post a few years back about fixing damaged
>> computers by replacing a one transistor that always blew.
>>
>> The inputs and outputs are pretty simple.  I went through this
>> too, and heres what I came up with:
>>
>> IDLE COMPUTER INPUTS:
>> Idle Switch
>> PS Switch
>> AC Switch
>> Hall Generator
>> Temp sensor 2
>> Power from relay
>>
>> IDLE COMPUTER OUTPUTS:
>> Idle air bypass
>>
>> Ideas?  Anyone?  Beuller?
>>
>>
>>
>> tabe johnson / 87 westy
>>
>> --- Larry Himli <lhimli@msn.com> wrote:
>>
>>
>>
>>> Bummer, I was so sure the relay would fix it....but no luck.  It
>>> still revs
>>> up to about 2K and at least it oscillates back and forth.  I turned
>>> on the
>>> air conditioning and it really revved up.  So now we have to try
>>> something
>>> else.  Have you studied the wiring diagram?  I will try to look it
>>> over and
>>> see what might feed the relay, etc.  At least it isn't raining
>>>
>>>
>>
>>
>>
>
>