I'm just going to describe this and hopefully someone has been there, fixed that. Upon starting (2004 C5, 6mn, 228/232 cam, 7500 miles) it idles rough for a bit then works its idle from around 400 up to 900. Then runs fine. I've been told that the rough start must be the battery not supplying enough power to the engine. It was tuned after the cam install and performs very well.

This is where I'm looking for advise. Battery is fully charged and only 6 months old - delco 86 - 3yr. I monitor the voltage within the DIC and it reads 12.5 volts with ignition on prior to starting. The car then starts right up, without any effort, with the voltage reading anywhere from 11.5 - 13+. After starting the idle drops to about 400, this is when the voltage drops to 11.5, the engine has actually stopped ocassionally, but usually stays running as the RPMs slowly climbs up to 900. If I try to help by feathering the gas, it only takes longer for the idle to settle at 900. Voltage then reads a solid 13.3+.

I'm told the tune is fine and the battery must be the issue. I thought that once an engine starts, it gets its power from the alternator, and only draws on the battery if the alternator is not suppling enough voltage.

Could the low idle cause the alternator not to generate enough voltage, therefore, needing to pull the shortage from the battery? Need I replace the alternator with a stronger one? If I thought it was a battery, I'd buy a new one today. But I don't want to waste my money on a battery, if it's just going to happen again.

As an aside, I went to Sears(near my house) to see about an Optima Red Top, and the book didn't list one because the 2004 model went from a 75 to a 86 code.

Any advise??

 

The low idle could be causing the problem or it could be the alternator.. If you have an Autozone near you, drive over. Ask them for a free charging system diagnosis.
Then will wheel out a Baer charging system analyzer, hook it to your car ,curbside and ask you to start it and idel it, then keep it a a certain rpm.
Within 5 minutes( for free) they will be able to tell you if you have a charging system problem .
Rich

 

Thanks,

I think there's one in my area, and I'll try it today.

 

If I decide to switch to an Optima Battery, which one fits an "04 C5?