Does anyone know the resistance reading of a good IAC (measured at "room temp" -- not hot)? Mine only measured 12.3 ohms which seems kind of low, but I would like to hear from someone whose has measured a good IAC to confirm my suspicions.

My Civic recently start flagging the IAC code. It does appears to run okay except for the idle just being slightly rough. I have a Helm manual (which does not spec that resistance measurement BTW) and did some debugging but now I'm down to the part where the book says to swap out a known good IAC and see if the problem goes away -- else swap a known good ECU. Well I don't have a spare IAC or ECU sitting around and furthermore those things aren't cheap!! The code initially clears after shutting down the engine because it take about 30 seconds after restarting the car before the Check Engine light reappears.

Any related info would be appreciated...

 

Clean your throttle body.

 

Actually I just cleaned the TB last fall. At the same time I also: replaced the plugs (with NGK), replaced the wires, replaced the cap & rotor, replaced the fuel filter, changed the oil, changed the tranny fluid, replaced the water pump, and replaced the timing belt.

 

Harumph! Sounds like your base idle is low.

Usually the IAC code is flagged when the ECU can't get your idle under control. 95% of the time it's because the throttle body is dirty, or the bypass ports are obstructed. It sees the engine idle speed and adjusts according to whether your idle is high or low. If it tries to adjust the idle and runs out of room to do so, then it just blames the IAC and throws a code 14 even if something else is the culprit. :eh:

What RPM is your idle when the car is warmed up? If it's low, scrape all the goop that Honda put over the Base Idle Set Screw on the throttle body, and back it out a tad. That will allow more air to get by the (bottom) bypass port, raising the idle, and taking the load off of your AIC a bit. If your idle is high, screw it in a bit. Once you have it in range, goop that screw again with some RTV or silicone. It keeps it from leaking air, or falling out.

The important thing is to match what RPM your hot idle is supposed to be. If it gets finicky, unplug the electrical connector from the AIC while making adjustments to the BISS screw and get it in range, then plug the AIC back in.

Another thing worth inspecting is the AIC ports inside its flange. Unbolt it, don't drop the gasket. It has a screen on the intake side, and it can get clogged if funk blew past your throttle body bypass. It's cleanable (is that a word?) with carb cleaner. Before you bolt it back on, take your intake pipe off and move it out of the way, then blow compressed air through the intake port (closest to the TB). Anything that could be blocking it should come out.

These things rarely go bad. I'd hate to hear that your're in that uncommon demographic. I know they're like $190 at the cheapest places because I had a lot of trouble with mine after I swapped my engine. After studying this thing for a month, I figured out I had the IAT and AIC connectors switched backwards.
:doh:

 

The idle did seem a bit low, so last night I backed out the BISS one full turn. Even after that, I still get flagged with the IAC code (#14) within about 15 seconds after starting the car. I will take your advice and take apart and check/clean those items soon -- hopefully tomorrow. I will report back...

 

Well last night I took off the IAC off and cleaned the screen. It was dirty, but didn't really appear clogged. I also cleaned the line and confirmed it wasn't blocked. Once I got everything reinstalled, I started the car again and still got the Check Engine light. I decided to read the code again, and this time it read 41 (which is a heated O2 sensor code). I don't know if I originally read it wrong or what, but the code was flashing "41" and not "14". I even had someone read the code just to make sure. I have noticed over the last several months that my fuel milage has dropped like 3-4 MPG. A bad O2 sensor could likely be causing that. So with this info, and the fact my car really does seem to idle okay (or maybe just a hair rough), I'm going to replace the O2 sensor with a universal Bosch one this weekend. Hoefully, that will fix my Check Engine light problem!

 

Isn't a code 41 the o2 sensor heater circuit? Code 01 is usually the o2 sensor circuit. You can probe the wires for the heater circuit on the o2 sensor with a multimeter to see if you have continuity. If you do, then the problem causing the code 41 is on your engine harness, not with the o2 sensor. 4-wire o2 sensors aren't cheap.

I can get you the wire info if you need it, as well as an ECU pin # and the locations of the wires on the bulkhead connectors if you want. I just have to dig it up. I only know this because I had to wire in a heater circuit to the ECU because my car did not have one on the engine harness. Checking it first is free.

Is this the original engine that came in your car?

 

Yes it the original 1.6L engine, and I actually have the Helm manual for my car. And yes you are correct it's the heater part of the O2 sensor that code 41 denoting. I was just generalizing it. I actually ran through part of the tests that the Helm manual suggested and didn't find any obvious problems. It did not have me check for continuity on heater wires of the O2 harness, but it did have me confirm that they were supplying 12V (well, battery voltage) when they should -- which should be just as good a check.

With my MPG notibly down and my Check Engine light indicating the O2 sensor (in general) I'm just going to get a new O2 sensor anyhow. I can get a universal Bosch one for $70 that I have to "splice" into the stock wiring (instead of spending $150-200 for the same sensor with a plug that fits the stock wiring).

 

Good deal! It sounds like you're on top of things. Just ensure that the tape and whatever you use to shield your splices isn't flamable, solder them, and keep those connections away from your exhaust manny and heat shield.

 

i actually have the same problem
and somehow replacing my cat with a high flow cat solved it.... for about two days
now its back