New Battery and now surging idle

[Slingshot]

The original battery expired on my '93 NSX after 9 years

I replaced it with a Die Hard Gold and when tightening down the positive lead, my ratchet contacted the battery hold-down rod briefly producing a spray of sparks. Everything works fine except my idle appears to hunt between 300 and 800 rpms. Does the ECU reset itself when the battery is disconnected and it takes a while to adjust to the engines conditions?

 

[Larry Bastanza]

Slingshot,

I am not totally sure about the idle roaming, but for future reference always connect the ground (-) terminal LAST, when installing a battery. It sounds like you connected the ground terminal first.

Also when disconnecting the battery, remove the ground terminal FIRST. This is the safest way. No sparks, potential fires, electrical damage, etc.

My $.02,

LarryB

 

[Kirthasa]

Keep in mind that the rough idle is normal after disconnecting your electrical system. I have seen it every time I have done so on my NSX, and several other owners have told me that it is normal as well. It has always taken a couple of days of driving before the idle and everything even out again - Nothing to worry about in my experience.

Aaron

 

[CityofAngels]

You would most likely not damage anything other than your battery. If it was only a momentary strike, then you're okay. I can't say that any of the dozen times I have disconnected my battery a rough idle has ensued. Very strange that some people experience it while others don't. You may find that it will relearn its idle or you could try disconnecting the battery again. Reconnect with less of a jolt - positive side first.

Let us know how it goes.

 

[nsx4fun]

For your sake, I hope everyone else's reply is correct and that time and/or a more gentle disconnect/re-connect of the battery cures your symptoms. But due to inductance in the battery, temporarily shorting out the positive side to ground and then releasing the short, can create very high voltage spikes. These high spikes are very capable of damaging sensitive electronic circuits, like the microprocessor that runs your car. This damage could be extensive (total death to the IC) or partial (where it kinda works but not 100% correct) which might be what happened to you.

Good Luck,

Fritz MSEE

 

[Slingshot]

Originally posted by Kirthasa:
Keep in mind that the rough idle is normal after disconnecting your electrical system. I have seen it every time I have done so on my NSX, and several other owners have told me that it is normal as well. It has always taken a couple of days of driving before the idle and everything even out again - Nothing to worry about in my experience.

Aaron

Thanks Aaron! I finally found time to test the anomally today. The idle was smooth at about 600 RPM and after about 15 minutes of driving, I realized my climate control was off; when I turned the climate control on and the A/C kicked in it started pulsing at all stops between 300 and 800 RPM! I took a 30 minute drive through residential districts loaded with stop signs. Now it surges ever so slightly between 500 and 600 RPM until the A/C cycles off and is smooth as glass at 600 RPM. One more 30 minute drive in a stop and go setting should tweek it to perfection

Bob

 

[nsx4fun]

Glad to hear things are operating more normal now. And I hope you've learned that it is not good to use a wrench on the positive battery post while the negative is still connected. you were fortunate that all you had was a few sparks. Not only can high voltage spikes be generated, but a wrench that gets wedged on the positive post and contacts ground can also cause sustained 600 to 1000+ amp current flows. Wrenches glow red, fires start, and quite often Batteries EXPLODE!!! In the future, please always disconnect the negative first and when reconnecting, connect the negative last. Life is always much better that way.

Fritz

 

[lemansnsx]

Originally posted by nsx4fun:
a wrench that gets wedged on the positive post and contacts ground can also cause sustained 600 to 1000+ amp current flows. Wrenches glow red, fires start, and quite often Batteries EXPLODE!!!

Just thought I should mention jewelry. Remove any before working near your battery! I met someone years ago who had been working on the battery while wearing the heaviest gold ID bracelet I've ever seen. The bracelet became wedged, the bracelet had a notch cut into it and the burn scars years later were still horrifying. Take the gold off!



------------------
Andrew Henderson
The NSX Model List Page

"We have long acknowledged that enthusiasm for things automotive is a sure
sign of emotional instability if not outright dementia" - Brock Yates

 

[nsx4fun]

While we are on the topic of jewelry horror story, I have heard of wedding bands cauterizing a finger to the point that the finger fell off.

Positive note, no bleeding.

12 volts sounds harmless, but 1000+ amps is no laughing matter.

 

[sjs]

Originally posted by nsx4fun:
While we are on the topic of jewelry horror story, I have heard of wedding bands cauterizing a finger to the point that the finger fell off...

Thanks!! I'll add that to my list of reasons to stay single.