Kindled Light

Hey, I have a 1999 Civic Si with a rather strange problem. Originally, I ended up receiving P0505 Codes for IACV issues where my idle would drop down to 1,000rpm after putting it in neutral coming to a stop, then jump up to 1,300-1,600. I replaced the IACV, adjusted the idle screw in the throttle body, and reset the ecu via battery disconnect and let it recycle with no load at idle for 10 minutes, and even bled air from the coolant.

I no longer get codes, however my idle still doesn't sit right. It will drop to 1,000, then 750 under no electrical load besides a radio. When I use my signals, headlights, heater, windows, itll jump in idle and dim the lights/dash for a split second and raise idle anywhere from 100-300. Now I had the battery and charging tested at autozone and it passed. It's only a year old, 500CCR Duracell Gold.

Am I missing something? Is it alternator related? I even replaced my grounds with Chase Bays 8 gauge engine to frame and transmission to frame grounds and a 4 gauge battery ground wires since my old ones were toast. That didn't fix it either. If the lights are on, it normally drops to 1,000, then 1,200-1,400, then back down to 900. When they're off, its 1,000-1,100, then 750.

What could be my issue? I feel lost.

Car: 1999 Honda Civic Si
Engine: B16A2
Transmission: S4C
Modifications: AEM Short Ram Intake, Cruise Control Delete, Walker OE Replacement Exhaust with Original OEM Cat.

tony_2018

bleed system, you've introduced air into the system when you replaced the iacv. bleed until it doesn't jump around, adjust idle, reset ecu, learn idle.

BiggieBert

Kindled Light

Base idle as the book says is 700ish + or - 50. 500 and below is too low for OBD2.

As for the system, I bled it post replacing the IACV as well. I'll try it again though.

mk378

Check your TPS calibration. The throttle plate stop screw is not to be adjusted. If you did adjust it, set it back so the throttle plate closes fully at idle. The air valve screw is to be used to set base idle speed.

If it's a two wire IACV, fully warm up the engine, turn everything else electric off, then unplug the IACV (which will throw a code) and adjust the air valve screw for a much lower than normal idle, but still running. If you can't get it to slow down with the IACV unplugged, there is an air leak somewhere. Of course the vacuum port where the cruise control attached needs to be blanked off.

Kindled Light

I do have the cruise port blocked off with a cap. It was the air screw then that I adjusted on the TB with the IACV unplugged. I can retry the test again though as you've described and see how it goes from there unless I adjusted the "wrong" screw.

Kindled Light

Yeah looks like I adjusted the Idle adjustment screw towards the top.

JRCivic1

This is the correct value to set the idle with the IACV unplugged.

750 rpm +/- 50 rpm is the normal operating idle speed. IACV is plugged in at this point. This is the proper rpm for setting the distributor timing as well.

Kindled Light

ahhhhhh, gotcha that makes more sense thank you.

Infinity_Racer

Kindled Light

It's definitely not the Idle Air Control Valve. I'm going to be reseting my base idle and doing some work on the car this weekend since I'm off. It's been quite a frustration, but at least it's nothing damaging from what I can tell so far. I have noticed my PCV breather box is pretty caked in oil so that's another project to check out as well. It could use a tune up as it is so that's on the list as well.

Infinity_Racer

Kindled Light

do you're lights dim like mine? I'm not an electronics geek so I never know what's what.

But I have to say this is absolutely insane. I'm going to be buying some basic tools like a multimeter, compression tester, timing light, etc. I've already done my plugs and wires before with NGK. I don't know what could be the cause personally. It's crazy that you have the exact same problem!

Here's a video of my car being put under basic headlight load and such. You can see the changes to the motor through the RPM. Who knows, maybe I have some secret vacuum leak or my car is literally possessed. I find it terribly annoying too.

Infinity_Racer

mk378

With the IACV unplugged, does it slow way down? If it runs fast with the IACV unplugged, something mechanical is letting too much air in.

If it does slow down with IACV unplugged, but then the ECU commands the idle too high when it is plugged back in, consider the TPS caibration and the ECT. If the ECU sees a reading from the ECT that the engine is cold, it will make it idle fast. This could be because the ECT is bad and its readings are out of specification (but not far enough to throw a code).

Also check all the sensor plugs by wire color make sure they are plugged into the right things.

This is all of course assuming that the CEL is not on and no codes are set.

Kindled Light

it's really just a soft dim. It's what I thought would be normal of anything this old as it is. i really wonder if we have a vacuum leak somewhere. If I get on it, it'll really bring it up (VTEC 6K plus), when I rest the car in neutral (1,400-1-550)

Kindled Light

when I originally did my IACV unplug test, it did drop the reva, and I could almost kill the engine with my finger on the hole as the manual suggests.

Just so I understand the acronyms, what does TPS and ECT stand for?

mk378

Throttle Position Sensor and Engine Coolant Temperature sensor.

If the high idle seems to correlate with flooring the gas, you should consider the maybe the throttle cable is sticky and doesn't let the throttle plate close all the way every time.

Kindled Light

I've wondered that but it's only based upon going high up in the rev band but I'll check that out as well.

Where is the ECT locates? I know the TPS is located on the back of the TB

Infinity_Racer

BiggieBert

Infinity_Racer

BiggieBert

Kindled Light

triple beam

clean your fuel injectors or replace
my idle was fluctuating and now its great