Any ideas on why this?

[Eheim]

Hi Guys
I recently had my NSX battery checked by a battery specialist which indicated after a full charge time
at 58% capacity. The load check on the alternator done at the same time was perfect.
Obviously with that poor battery result the next move was to replace it.
Surprisingly the car now idles really smoothly at around 900rpm whereas before it always used to have a pronounced hunt
at idle - continually oscillating between 600 and 1200 rpm - especially when cold.
I have previously disconnected the old battery for recharging a couple of times as well as removing
the clock fuse to reset the ECU and these resets have never improved the idle so I can't see that the ECU reset figures in this.
So interested to know if anyone can explain why simply replacing a battery could have this result.

Cheers John

 

[rwdforlife]

sounds like an alternator issue.

 

[Larry Bastanza]

Year car? 3.0 or 3.2?

 

[Eheim]

Year car? 3.0 or 3.2?

Hi Larry - 1991 - 3.O - 100,000 km's (63,000 mls)

 

[Grimeas]

Maybe weak battery corrosion on terminals wasn't allowing good power flow to the coil packs giving weak spark?

 

[Eheim]

Maybe weak battery corrosion on terminals wasn't allowing good power flow to the coil packs giving weak spark?

I think that possibly you could be right. The new battery terminals were a really good tight fit and with the old battery
being weak perhaps the alternator doesn't provide enough at idle revs so leaving the coil packs to rely mostly on the battery at idle.