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Discussion Starter #1
I'm helping a friend hunt down an idle problem, and we can't seem to figure out the cause. The problem originally manifested itself as an idle surge before the engine was warmed up, although recently it has started surging when warm as well.

(Before you delete/move this post, please read the questions at the end... :) )

She's fixed the idle switch (contacts were dirty and it wasn't functioning) and adjusted the idle per the manual procedure. I think she pressure-tested the intake for leaks. The ISC coil resistances check out. However, she's noticed the following unusual ISC behavior:

  • With the ignition key "on", all accessories off, engine not running, it reads 96 steps
  • Turned ignition off and back on, still reads 96 steps
  • Then, started engine without touching the throttle, and it slowly drops to zero
  • Turned engine off, logger shows 96 again
Is the engine-off 96 reading considered "normal" behavior? (Obviously the ISC dropping to zero is not right.) I would love to check it on my own vehicle, but it's uh...disassembled right now. ;) The manual doesn't go into this type of detail, and I can't seem to find any posts on this particular information. The manual also lists a whole bundle of possible causes, including a faulty ISC motor, but it seems to check out...

Anyhow, any assistance would be greatly appreciated!

Erik A.
#206/1000
 

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I was having a similar problem a while ago. It turned out that before I replaced the caps in my ecu they had leaked. The driver circuitry for the isc and the injectors is right there and was damaged.. I would try swapping ecus temporarily and see if that helps. -mike
 

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Discussion Starter #3
rmgreen13 said:
I was having a similar problem a while ago. It turned out that before I replaced the caps in my ecu they had leaked. The driver circuitry for the isc and the injectors is right there and was damaged.. I would try swapping ecus temporarily and see if that helps. -mike
That's a good thought...but when the caps were recently replaced, the old caps weren't leaking and the board looked fine. Aside from the idle problem, there don't seem to be any related quirky issues like leaking caps often cause...

So, nobody has ever checked the ISC steps with the engine not running? It's easy to do...please? :D I would do it, but I still don't have my car back together (it's more apart now than it was yesterday...)


Thanks,
Erik A.
 

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hi, when I originally changed my caps the board looked fine. I only discovered the problem by watching the isc with a pocketlogger. Th #96 sounds familiar to me, this all happened a while ago and I no longer run stock engine management, I switched to Haltech. In any case the circuit boards are multilayer and can easily be damaged and look fine -mike
 

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I am fixing the exact same problem as we speak. I have also followed the same procedures as you with two results : The ISC is somehow faulty despite the proper resistance between coils and this has shorted the related circutry in the ECU. My CAPs appear fine, but on the back-side of the board there is, what appears to be, some kind of corrosion or burn tracks. This does not seem to be caused by anything from the top-side of the board. I also inspected an ECU from another car that ran perfectly fine and it had the exact same appearance. So what does this mean? I don't know, but the ECU defininitly cannot controll the idol in my car. Foreignecurepair.com lists some info on daignosis that may help.
In any case I am going to replace both parts. I'll keep you updated.
 

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Discussion Starter #7
Blackboost said:
Gonzo...

Try swapping you ISC in her car and see if it works correctly. If it doesn't work, try swapping your ECU in there and see what happens.;)

Hehe...umm...we don't actually live in the same state. But your advice is sound--I think that's where she's headed...(?)

Thanks,
Erik A.
 

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I just put in a new ISC, and another (used) ECU with the same result. I think the other ECU is bad as well. The EFI module buzzes when I turn on the ignition. So, I just ordered a rebuilt ECU. Cross your fingers.
 
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