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Thread: Bad ISC or ECU?

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    Devoted Darkling Feedback Score 0 ukyo's Avatar
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    Bad ISC or ECU?

    Hi all. My VR-4 has been acting up for a while now. The factory ISC appeared to have died about a year ago. I got a replacement from eBay (risky move, but the price was right). It ran fine for a few months then the engine began to stall out just like it was doing with the original ISC. I complained to the seller and they sent me another one. The new one lasted about 2.5 miles from my house before it gave out. Done with eBay, I got a new unit from Ninja Performance. It worked for about a week before it started doing the same thing. Am I really this unlucky with ISCs? Can a failing ECU mimic the symptoms of a bad ISC? I pulled the ECU out and looked it over, but I didn't see any obvious capacitor issues.

    The oddest part is, the car will sometimes run and idle just fine, then out of the blue it will try to stall out, and will stay that way for weeks on end. Then suddenly it'll run fine again... rinse and repeat. Any ideas will be appreciated. Thanks!!!
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    A bad isc can actually fry the ecu.

    J.R.

  3. #3
    Devoted Darkling Feedback Score 0 ukyo's Avatar
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    Just to update here, it looks like I found the problem. It wasn't the ISC / IAC at all. It was... THE BATTERY. It had been slowly dying on me, but was still starting the car so I thought everything seemed OK once the engine was running. The voltmeter read 11.8v on the battery when the car was off. I thought it was still good...

    The battery finally died and I replaced it. The car has been perfect since (well, minus the rusty nail I picked up in my driver's side rear tire). So there you have it. These cars are crazy. They can mask the root of the problem by presenting a failure in a known trouble spot just to mess with you. Live and learn.

    My next investment will be a battery tender. I don't drive the car enough to keep the parasitic draw of the on-board electronics from damaging / killing the battery over time. Or... novel idea... I could drive the car more???
    Last edited by ukyo; 12-20-2017 at 09:35 PM.

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    Thanks for the update.

    11.8v is considered almost zero charge remaining and 12.6v is fully charged. Those readings/statements are only valid if the battery has been sitting there for a while without being charged. Incidentally I recall weird electronic related things happening to my car also, for me it was the alternator nut not tighten down enough -- even though it ran fine for 3 years earlier when it was replaced. First my aftermarket radio refused to power on, and then it was something else, I wish I remember what it was. lol.

    Edit: I use a large wing-nut for my negative battery terminal and unplug the two ground wires when the car is sitting -- stops the parasitic current draw during the winter.

  5. #5
    Devoted Darkling Feedback Score 0 ukyo's Avatar
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    I think I'll copy that wing nut idea. I'll have to put the radio code in and the car will have to relearn the trims, but that's better than slowly killing the battery.

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    I drilled a hole on my wing nut end, attached dental string to it, and the windshield washer hose. This way if I accidentally drop the wing nut it's not lost in the engine bay somewhere.

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