99 Civic. Whacko battery.

Hello all. Wow, I was gone for a little bit. Things have been busy at the shop with tax  returns rolling in.

I was on my way back to the shop yesterday after having lunch with my wife, when my head installer calls me on the cell and says that a guy came in with a little '99 Civic looking to upgrade his battery. He already had a setup in his car for a couple of years, but wanted to rid himself of some minor dimming issues he had been having for a while. So my guy sold him and installed a big Optima Yellow Top, the kind we usualy put in SUV's.

Well, apparently, the car refused to idle above 500rpm with this big battery in it. I got back to the shop, told the customer to go ahead and drive the car around for a while, since the computer needs to reset after having the battery unplugged, and if that doesn't work to bring it back. He comes back in about an hour and the car is holding a solid 500rpm. My expierience with these cars is that they normaly run at  600-650 at idle with an automatic and no accessories (My daughter has one). Turning the headlights on should make it rise to 750-800. We put the headlights on, had his bass turned up, everything, and the idle refused to rise beyond 500.

Needless to say, the guy was freaked out, so I went ahead and took the battery back and told him I would look into it.

So here I am, looking into it.

Any ideas, guys? I own a stereo shop, I'm no automotive electrician. =(

So you're saying that once you put his old battery back in, it started idling normal? Did you try another Yellow Top you have or maybe try the 51R Yellow Top which is the Honda type and see what happens? BTW, his idle should raise even with a full load because thats what the idle control valve does in these cars - it detects when the idle has dropped below the set rpms and it raises it back up.

I noticed with my Civic, if I suddenly turned on the headlights and fogs while holding the brakes, the idle would drop for a second and then quickly bring itself back up to the correct speed. Then if I shut everything off, it would go a little higher for a second and then come back down to normal idle speed. Thats the IACV or Idle/Air control Valve that does that - maybe his is not working or disconnected??

Its close to the throttle body on the lower rear part of the intake manifold.