Hello, I just started my S2000 tonight and I noticed that when it is idling and I rev it (2k-4k rpms), when the revs descend the car almost dies. I just replaced the battery recently, but I have not been driving it. I have not gone more than a week or so without starting it. I noticed that when the lights/headlights are turned on it seems to almost die after reving, but when they are off it is not as dramatic. Does anyone have any information on this? Thank you for your time!

 

everytime you disconnect your battery, your car will not idle the same way. you need to let it idle for a good 10 to 15 minutes so your ecu can relearn its idle spot.

 

Stop revving it.

 

Are you sure the battery is fully charged? Sure it was even fully charged when you bought it? I say get/borrow a good charger, and fully charge the battery. Then try again.

Are you sure the charging system is OK? Why did you replace the old battery? Maybe the battery wasn't the problem, maybe the charging system was not charging the battery, or the charging system wasn't working well and it took out the battery. Get a volt meter, and check the voltage at the battery at, say, around 3K rpm's. It should be like 14.5 volts or so (not certain for S2K, but this is a general value for most cars).

Check charging system, fully charge batt, I bet your issue goes away.

 

This and as mentioned by franky if you disconnected the battery the ECU will need to relearn idle (check link below).

https://www.s2ki.com/s2000/index.php...&t=549159&st=0