[T3] cool weather idle hunt

Jim Adney jadney at VWType3.org
Tue Jan 17 19:08:39 PST 2017

On 17 Jan 2017 at 20:55, Daniel Nohejl wrote:

> Anyway.....as to the ECU....If plugging in a new one started the the
> engine up and got me home and plugging, unplugging, and re-plugging
> the old one only produced (or re-produced) a no-start situation, how
> could it not be an ECU issue? I know the ECU is supposed to be "bullet
> proof", but I sent Jim a bunch (5 IIRC) of ECU´s with issues rang?ng
> from oewonTMt ?tart the motor to oedoesnTMt ground the fuel pump and
> only one was fixable. The ECU I removed today was one I bought from
> Jim and installed in July and now it seems to have oedied which leaves
> us with one backup ECU and thatTMs one that Jim re?aired so tha? it
> would ground the fuel pump relay. 

Only driving hours will tell if changing brains got rid of the 
hunting idle that you had. It seems pretty clear that there's a 
problem with the brain you switched out. As for your question of is 
this a "thing," I don't know. I've never had it happen, never heard 
of it. I'd expect failures to be more sudden and complete, but who 
knows. I'd also expect any brain failure to affect both idle and 
general driving.

As for aging capacitors, there are no electrolytic caps in these 
brains. Bosch was smart enough to avoid them. The types that are in 
there should last forever. Transistors are more likely to have an 
internal bond failure, expecially the ones in the metal cans; the 
more modern epoxy style seems to be much less prone to failure from 

If you're willing to send me the brain that failed, I'd like to see 
if I can find the bad part. I might even be able to replace it, using 
parts from one of your non-fixable brains that I still have here. I 
also have more tested-good B brains.

BTW, I know I still have parts of yours here that I need to bill you 
for and send to you. My apologies, but I've been under the weather 
for the last 5 weeks and am finally starting to see daylight. It's 
nothing serious, but it's left me lacking in energy in general and 
enthusiasm for dirty VW work in particular. I'm finally getting back 
into the grind. Sorry for the delay.

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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