I know lots of people ask the same? and i did search but most were on built motors or not same problem. Ok i have a 99 civic ex stock moter 56,500 miles. The idle is starting to drop. like it used to idle just below 1000 now its dropping to like 400-500 or something. Its doesnt stall out though. does anyone know why this might happen. no ecu codes. I have a CAI and a Catback exhaust as far as performace.

 

Have you done a tune up lately? Try playing with the iacv, it's right by the throttle body. Use a flathead screwdriver to adjust it. But I would recommend a tune up. New cap, rotor,plugs and wires...

 

it has a new cap rotor and plugs but stock wires could that be causing the problem

 

You replaced everything but used the old wires or did you replace that too? OEM ignitions wires are pretty decent and I doubt it that it's causing the problem.

 

no it still has the old stock wires

 

I doubt its the wires. Sounds like incorrect gap on your spark plugs. Check to make sure you didnt unhook any vacuum lines when installing the intake (stranger things have happened). Also, is the idle rough or is it just really low. Does the car chug/stutter when accelerating at all? how old is the fuel filter. My suggestion-go get a tune-up, it doesnt sound like anything major, though.

 

it accelerates fine it makes the car vibrate though. Fuel filter is also kinda new. the intake has been on for a while problem just accured

 

the car vibrates at idle? check your motor mounts. Also, recheck the gap on the spark plugs. Listen to the motor, do you hear any "hissing" sounds coming from anything besides the intake?

 

spark plug gap has very little to do with the idle 'dropping'. sounds like IAC not recovering idle quick enough.

This may be able to be fixed as simple as resetting base idle to spec. Try doing a search on all the idle issues in here. I know that I have continuously described (in detail) exactly what to do a few times.

Let me know...

 

wouldnt the IAC cause the acceleration to be jerky like I asked?

 

its not jerky i have motor mount inserts but it never dropped before. no hissing except the intake.

 

IAC wouldn't necessarily cause engine jerking on accel.

 

like i said it doesnt jerk just drops idle and vibrates the car

 

hmmm...man, it could be a number of things (timing way off, clogged up cat, idle screw) I would just do a complete tuneup, and if it doesnt fix the problem, take it to a mechanic to diagnose the problem. Good luck, I hope everything works out for you.

 

thanks i guess ill try to figure out something if anyone has anyother ideas let me know

 

the proper thing to do is to not just start throwing parts at the car in a poor attempt that something will change it. Timing won't really cause idle issue with fluctuation. Clogged cat would generally give no power on accel. I think you should still try setting base idle first and see where that gets you for starts.

 

sorry what doyou mean base idle?

 

It is the idle the engine is supposed to run at with no accessories on and with engine at operating temperature.

Spec is 700-750rpm. you need to check the idle speed with an inductive tachometer or timing light with built in tach. (factory tach in dash is too inaccurate for this procedure.)

Start with getting engine up to operating temp.
Next, disconnect IACV and see where idle speed is. (if idle does not change when IACV disconnected, idle too high: if idle speed drops to the point where engine stalls when IACV disconnected, idle speed set too low.)

There is an idle set screw located in top of throttle body, may have some gray sealant over it, this is what is used to set base idle. If engine dies when IACV was disconnected, turn screw counterclockwise about a turn and a half and restart engine.

Next, hook up your tach.

With tach hooked up, turn idle set screw clockwise to lower idle or counterclockwise to raise idle.

The base idle with IACV disconnected should be 500-550rpm, no more than this or less than this.

When you are confident that it is set to this specification, turn off engine, reconnect IACV connector, clear ECU codes, and restart engine.

With all accessories off and engine still at operating temp, engine should now be idling at 700-750rpm.

Hope this helps

Let me know if there are any other questions I can answer for you...