Hi, Ijust gota 98 Civic EX about a week ago, and I've noticed that when I stop, it idles at 1,000 RPM for about 15 seconds, then it drops QUICKLY to about 100 RPM and stays there until I go again. It doesn't sound like its struggling, but I mean, its only 100 RPM. Should I adjust the idle, or is that normal for a 98 Civic?

 

100 sounds pretty low, its not turning off? it usually idles higher than that, but lower than 1000 is fine.

 

I know lower than 1,000 is fine, but its idling so low I'm suprised it isn't dying at every light. Its perfectly steady at 100, it it dropped even slightly I think the car would die though. Its just... weird.

 

I think it's running normally but your tach is not reading right. Below about 500 the whole car will shake, and much below that the engine will stall. It is simply not possible to actually idle at 100 rpm.

The idle is controlled by software in the engine computer and is not adjustable.

 

That isn't true at all. There is a screw on the throttle body that is used to adjust your idle speed.

 

Yes that screw does set the limit on how little air will enter the engine, but it isn't intended to control the idle speed, which the ECU will attempt to do with the IACV. If things are working normally inclucing having the screw within a wide range of acceptable adjustments, the idle speed will always be the same. Trying to alter the idle speed from what the ECU wants will set the CEL.

So the bottom line is someone like the OP who doesn't experience stalling or over speeding at idle, would do best to not turn that screw.

 

See, thats the main thing that got me. It doesn't sound like its struggling at all, it sounds just fine. My last car (93 Honda Accord) had a similar problem, it would idle at a nice... oh probably 650 RPM, then it would dip down to about 300 for a second, nearly stall, then go back to 650. My Civic doesn't sound bad when its at 100, it hasn't stalled, it starts right up... meh.

Well, I have to take it in to the shop on Monday for another problem - the thermastat isn't working and my car keeps overheating in stop and go traffic. So, I'll see if they think its the tach or not.