2ToneEM1

Hi all, I have a 99 civic si and recently has started idling very badly, when at idle it will rev between 1000-2000 several times then even out at 1500 (usually doesnt show a CEL) and sometimes it will rev quickly between 1500-2000 (will always show CEL)

Shows CEL p0505 and only does this after driving, not on start up

Tried cleaning the IACV but it didnt help any

B18C5-EH2

First thing to do is check the idle mixtrue screw on the throttle body.

Remove it with a flat blade screw driver, and clean the tip free of any carbon deposits (black junk) on the tip.

Screw the screw back in and set the base idle if possible. I would try to get it as close to how it was prior to removing it and cleaning the tip. I'm suggesting this to clean the tip, not to try and adjust the idle per say since I doubt the screw itself moved to cause your idle issue.

After you've made sure the idle mixtrue screw is not dirty warm the engine up and after the fan kicks on a few times (to let you know the car is at op. temp.) unplug the idle air control valve - it's located on the back of the intake manifold. If the idle does not change whatsoever when you unplug the IACV then you need to replace the IACV. Crappy part is that it's a pretty pricey part, and NEEDS to be purchased brand new from Honda, not Auto zone or NAPA.

i.

k check this out, and this is from experience, (recently) my post on my problem might still be on the first page, so you can benefit from this...

First off, the code you're getting (P0505) same as CEL 14, is not IACv like how it says in the FAQ's stickied in here, Club Si, etc...

P0505/Code 14 is Idle Control SYSTEM malfunction, not IACv.

Possible Causes:
IACvalve mechanical malfunction
Throttle body clogged port, improper adjustment
Intake manifold gasket leakage
Intake airhose loose leakage
Vacuum leak
ECT sensor incorrect output
Throttle Posistion Sensor incorrect output
(for the TPS incorrect input, this might be only for motors made in '96)

Try an check these things.

Start the motor, hold rpms at 3000 until the radiator fan comes on, then let it idle.
Check TPS, with the throttle fully closed, the TPS should be around 10%
(coolant temp should be around 200 degrees, give or take 5 degress or so.)

if your idle is 550 or less, check for vacuum leaks. Take the intake off, put your finger over the lower port in the throttle body. if the idle doesnt drop, check for vacuum leaks, make sure the throttle valve is closed completely.
if the idle does drop, adjust the idle speed. if you cannot adjust, replace IACv.

if idle is normal, disconnect the connector from the IACv. if the engine speed doesnt increase, replace IACv.

if the engine speed drops or stalls, adjust the (base) idle speed, clean the ports int he throttle body is necessary.

Do these before you decide to go down to Honda and spend $290 on a new IAVc and you dont need it. But if you do, i have one, brand new in box that i cant return, so its for sale.

(btw, this is the kindo of post i was looking for, but couldnt find, so here you go)

2ToneEM1

Thank you both for the info and ill try all of it firs thing tomorrow

B18C5-EH2

Yes the info above is good info for sure.

The only thing is he probably doesn't have any way to actually check the TPS sensor.

The reason I suggested making sure that the idle mixture screw was clean, then unplugging the IACV was because usually vacuum leaks don't just occur. unless he has done work to the car recently like an intake manifold swap, etc.

I wouldn't think it's a vacuum issue. It's not impossible, but more likely that he's got an electronic problem (like the IACV) or the mixture screw is finally dirty enough to impair the idle.

I certainly agree with trouble shooting like we're suggesting before just saying "it's your IACV homie. My boy's Si did the same thing y0!" $200.00 later and it still idles whack, and then he finds out it was a simple idle adjustment/dirty screw or something, and that would suck.

2ToneEM1

It could be the intake gasket, a few weeks ago i burnt 2 valves and after i got it back it ran fine for about 2 weeks then started this.

B18C5-EH2

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 2ToneEM1 &raquo;</TD></TR><TR><TD CLASS="quote">It could be the intake gasket, a few weeks ago i burnt 2 valves and after i got it back it ran fine for about 2 weeks then started this.</TD></TR></TABLE>

Ahhh!

Well when posting topics about check engine lights or any running order issues it is always important to list work done recently even if you might not think it's relevant.

You having said that would change my answer completely now.

I'd spray some carb cleaner around the circumference of the IM gasket and see if the idle changes - if it does then you've got a vaccum leak there.

Hell you really need to recheck every vacuum line associated with the IM now.

2ToneEM1

Thanks, but already tried that and there was no change in the idle. But ill try it again just to be sure.

Probably wont help and but sometimes i also get a cel for system too rich, i dont ever get it at the same time as the idle system malfunction but every now and then it will pop up, but im pretty sure its because i have a b&m adjustable regulator.

B18C5-EH2

System too rich (P0172 I think?) can be caused by improper valve adjustment too. If the head was odd recently you might want to check the valve lash settings.

2ToneEM1

Hmm, cant remember if thats the code it shows or not, ill check and see if its still showing it, shouldnt be valve adjustment, after the head was put back on i took it and had the valves adjusted.

2ToneEM1

Found the problem, the wires on i think the ECT had been cut, so crimped them back together and problem solved.