The Never Ending Low Idle Issue

[MattR1995]

Please no use the search function replys I have used it and google literally millions of times I have done every suggestion on any thread I have ever read with no results to helping my issue. I tried to be as detailed as possible please someone help me out.

Car Info:
2000 Civic EX EJ8 D16Y8 5 speed manual completely stock motor

Not sure what real mileage on car is they were rollback according to Carfax in 2011 car was reported of having 145k miles. I bought the car in 2013 and odometer read 135k fast-forward a year now reads 147k so I have personally put 13k on it. I know the transmission is not original to the car due to the VIN plate on the trans does not match VIN on car.

I have no misfires on any cylinders the car accelerates fine normal power for a D16 no hesitation nothing out of normal.

Car idles low dipping all the time to 450-500 causing the car to shake and you can see it trys to shoot back up for a good 2 secs but just can't and stays low idle shaking the whole car.

For the life of me I cannot find the problem to my on going idle problem. As for most people when cold idle is completely fine no issues at all and as it gets to operating temp all hell breaks loose. Also to note the car seems to always run better at night time when the air is cooler. And there is no CEL on and yes CEL does work. What more could it be that I haven't already done?

Things I have already done:

-Cleaned IACV
-Clean Throttle body
-Checked Ignition Timing
-Checked "ALL" hoses for leaks (which to my knowledge wouldnt make sense anyways sense more air introduced to the engine would cause high idle/surging idle which I DO NOT HAVE)
-Changed Brake Booster and Brake Booster hose (idle goes really bananas when brakes are also depressed at idle based off testing thats what I concluded too but no help)
-Changed Spark Plugs
-Changed Wires
-Compression test done all cylinders were 165
-Seafoamed
-Changed PCV Valve and hose (the hoses was so worn it would collapse on itself (or pitching itself if you will) from the Vacuum.
-Adjusted Idle Screw(The right way right out of the Haynes, I only write this cause I just read so many threads of people doing it wrong and just want to clarify I did it to spec right out the Haynes)
-Throttle cable is fine
-Butterfly plate shuts properly and no gunk blocking it (cleaned it)
-Bleed Coolant
-Checked all nuts to make sure nothing was loose(Intake manifold nuts, throttle body, IACV, etc.)
-Clean Fuel Injectors (just your typical STP s**t I know these things have there hits and miss but just throwing it out there cause I did try it)

Really from what I can think of the only thing I haven't done yet is:

-Test TPS sensor (don't have multimeter)
-Changed or test Primary o2 sensor (from what I read these things just can be clunky and a lot of times no CEL goes since they still are technically working but not as well as they should be)
-New Ecu

Anything else I'm missing and info is much appreciated the annoyance low idle and occasional stalls are just so frustrating.

 

[nd4sped]

I had this very same issue and turned out my alternator wasn't putting out enough amperage at idle. This low amperage actually damaged my battery over a long period of time. Ended up replacing the battery later with a Optima Red Top I had.

Once the rpm was up driving around was pretty normal, on a rare occasion the car would have a weird hiccup but them continue on like nothing happened.

 

[MattR1995]

I had this very same issue and turned out my alternator wasn't putting out enough amperage at idle. This low amperage actually damaged my battery over a long period of time. Ended up replacing the battery later with a Optima Red Top I had.

Once the rpm was up driving around was pretty normal, on a rare occasion the car would have a weird hiccup but them continue on like nothing happened.

I have given some thought about my alternator especially since one day for no reason while I was driving the SRS light was just blinking at me no idea why and never happened again ever have that?

 

[nd4sped]

I have given some thought about my alternator especially since one day for no reason while I was driving the SRS light was just blinking at me no idea why and never happened again ever have that?

An easy test of your alternator without tools is to turn on all your accessories, everything. Then disconnect the battery. If it dies then there is an issue with your alternator. Now obviously if your idling low while doing this test it will most likely die.

Most part stores will test your alternator for free and those tests are generally trustworthy.

 

[MattR1995]

An easy test of your alternator without tools is to turn on all your accessories, everything. Then disconnect the battery. If it dies then there is an issue with your alternator. Now obviously if your idling low while doing this test it will most likely die.

Most part stores will test your alternator for free and those tests are generally trustworthy.

Alright I'll get both of those done tomorrow and write back with results yeah the problem with those services for free is I live in CA and for some reason all the free services autozone provides everywhere they can't do in CA not sure why some labor law I think? Anyone know if O'Reily's or Pep Boys will do it for free?

 

[surfingisfun001]

I had this same problem. Replaced the IACV and the problem went away. I'm not too auto-savy but I do believe they said at the shop they tried cleaning and soaking it overnight before changing it but that didn't help so they replaced it. It has been running fine since.

 

[XpL0d3r]

As for most people when cold idle is completely fine no issues at all and as it gets to operating temp all hell breaks loose. .

I had a similar issue. It was one my o2 sensors being faulty.

When the car is started from cold, it runs open-loop, meaning the A/F ratio is controlled solely by the ECU, disregarding O2 sensor readings. When the car warms up, it switches to closed-loop and bases the A/F ratio on the feedback that it gets from the o2 sensor.

For me, the issue was a faulty o2 sensor that was still working... just incorrectly. I never got a CEL because as long as the secondary sensor reads lower than the primary, it assumes all systems are working and that the cat is doing its job. It then takes those inaccurate readings and sends them to the ECU, thus giving you a wacky A/R ratio.

If the alternator ends up being fine, before purchasing another o2 sensor, see if you can find a known working one as a test.

 

[MattR1995]

I had a similar issue. It was one my o2 sensors being faulty.

When the car is started from cold, it runs open-loop, meaning the A/F ratio is controlled solely by the ECU, disregarding O2 sensor readings. When the car warms up, it switches to closed-loop and bases the A/F ratio on the feedback that it gets from the o2 sensor.

For me, the issue was a faulty o2 sensor that was still working... just incorrectly. I never got a CEL because as long as the secondary sensor reads lower than the primary, it assumes all systems are working and that the cat is doing its job. It then takes those inaccurate readings and sends them to the ECU, thus giving you a wacky A/R ratio.

If the alternator ends up being fine, before purchasing another o2 sensor, see if you can find a known working one as a test.

I checked alternator and its in good working condition and the primary o2 sensor was gonna be my last resort cause those were always a hit or miss thank you for that information though I have yet to read that on any site I will definitely be seriously looking into the o2 sensor thus everything has not worked. Thank you for the suggestion!