Sometimes after my car reaches standard operating temperature the idle will bounce from 1000 to 1500rpm over and over (sometimes when its not at tempurature but not nearly as much). What causes your idle to do this?

 

could and would most likely be a vacuum leak... check ur hoses

 

I had this problem when I bought my Si (used).. turned out to be a damaged/broken Idler Control Module which regulates idlling RPM. Had it repaired under warranty.. you may want to check on this.

 

I bought mine used howerver it was honda certified and did get the extended warrenty. im now making a list of all the minor problems (has no majors) and figuring out which ones will be covered by warrenty, sounds like both these causes will be thanx honda!

 

That sounds like you have a bad IACV (Idle Air Control Valve) or it may just need to be adjusted, which can be done by the twist of a screw (i believe) See if adjusting it helps, before you just go and replace it.

 

Could be an intake manifold leak, loose vacuum hose, or if you've done some major work to your engine that involves plugging/un-plugging electrical parts, you could have the harnesses of the AICV and IAT sensors crossed. Same plug. Usually accompanied by a check engine light with code 14 if that's the case, though.

If too much air gets past the throttle body or if there's a leak and your engine revs too high, then the ECU will kill ignition to drop it back to where it's supposed to be. The ECU won't do this until the car warms up and goes into closed loop. If one of the sensor doesn't report properly, the ECU stays in open loop attempting to correct the problem.

Low coolant can cause it also. Or a bad coolant temp sensor. Usually that will trigger a check engine light also.

No check engine lights, eh? If not, then do a search for "intake vacuum leak".

 

No check engine light, no modifications done, all fluids and filters and all that good stuff is up to date (including coolent), nothing has ever been unplugged since if had it, bought it at 44k and now it has 46k on it, im guessing it is iacv or icm, doubt its vaccum leak. thanx guys!

p.s. I put NGK Laser Platinum plugs in it ($40 that i find well worth it in combination with premium gasoline by the way)...that wouldnt cause it would it? I had them special ordered so i know they were gapped correctly.

 

I have the same thing now that I have an exhaust leak on my exhaust manifold.

 

Putting Premium gas in your civic will do absolutely nothing except break your wallet. There is no need for it whatsoever. Civics actually run better on what they are made to use, which is regular unleaded. It's built for the intentions of fuel economy, and people always seem to have this sense that premium gas will make it run better. It actually makes it run too rich if anything.

 

My car is N/A with many upgrades, it runs best on unleaded plus... which is 89 octane gives me the best Power and fuel economy.. If I use 87 octane, it gives me poor performance good econ, and with premium 91octane, good performance poor fuel econ. Hopefully my VAFC2 will give me even better power n fuel econ.

As for the idling issue, seems like a vacuum or Intake Manifold leak.