1996 Honda Civic DX High Idle Issue Questions / Optional Story

CSIT_Civic

New Member
To shorten things up, from writing the essay below, I have obtained a couple questions:

when the iacv is unplugged but is letting in too much air, what does that mean? is it stuck open? I thought when there is no signal to the valve it is supposed to be closed. I can only get my idle low enough for adjustment when the iacv port inside the throttle body is plugged. The valve is new and clean so I am not worried about it being broken, I did reuse the old head gasket because the new one did not come with one and my local stores did not have a gasket in stock. :/

I can not figure out this high idle issue, all the information I can think of is listed below, I would greatly appreciate any hints or starting blocks I go off of because at this point I'm just tossing things around and killing time. Learning a lot though in the process and hope to learn more!

(this was written at a different time lol)

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Dont have to read this unless you want to kill some time or need more info!

Greetings form mates!

Have a bit of a head-scratcher here I am wanting to get some insight on. There are many idle writes ups out there and I have done my searching, however, I feel like everyone's problem is unique and there are many different combinations of engine setups. I think mine here is different and hope one day someone else can benefit from this. I am going to try and be really specific because this car is a mess... Almost want to get a whole new engine. I am also going to use this as a log for myself as well so I can think more about the issues while try I write about them it and organize what I have done so far.

The Vehicle:

1996 Honda Civic DX Coupe
Car Has ~175,000 Miles
Automatic Transmission: d16y7
Engine Block: d16y7
Engine Head: d16y8 / P2J-2
Intake Manifold: d16y8 / P2P IPT-4
Distributor: Stock one plug model
Throttle Body: GY? not sure where it's from but it is an automatic one with the IACV on the bottom
Fuel Rail: y7 rail: p2ra620 -390941
ECU: stock ECU - p2p (can get an exact code later if needed)
Axle back exhaust
AEM air intake - w/ carb stickers

Generally, the car followed a regular maintenance schedule and with this set up was able to pass smog at one point.

Am I missing anything else?

Currently, the car is not registered (2016) because I need to smog it, but can not with the idle issue. Everything else has checked out fine.
The windshield is cracked, my fault, forgot the hood was not latched and went for a drive, wind flipped it up pretty fast.
I have made a lot of cuts in the wiring harness over the times for a remote starter system, gauges, and all that good stuff. Since then, all has been removed. Literally restored it back to stock condition with black tape, so nothing aftermarket is messing with the car.

When I first bought the car, somehow, ~ 7 years ago I broke the check
engine light, I do not know what I did but it does not cycle when the car turns on or light up when there is a code but the system works fine and when I check for codes it triggers and clears codes like a normal system. For smog... this is a little bit of a hack here, but I just spliced the D4 light to the check engine light... and well there you go it "works", passed smog.

Did not need to know that for the idle issue but I wanted to share a good way to get around being blocked from smog if you have no codes and a nonfunctioning light for some reason.

So how / when the idle surge started:

On my radiator, the plastic nozzle for the overflow tank snapped off, glue worked for sometime but eventually I replaced the radiator. I also swapped the rocker the throttle cable attaches to. Since I swapped to a y8 the angle has been off and I have been wanting to fix it. Feels a lot smoother now on the foot now. However, since then I've been experiencing an idle surge.

How it surges:

The car will have a cold idle between 1100 - 1500 rpms, it will stay up there until the thermostat pops and the engine is up to temperature. Then the car will realize its rpm is too high and start to cut the fuel injectors and create the nasty surge.


What I have tried to fix it / what I have checked:

Coolant temperature sensor works

Coolant switch works and fan will turn on and cycle when needed

Timing is accurate: 12 degrees last smog, and has not changed since, I would check it but I am unsure how to with a surging idle.

The system is bled, I am more than confident there is no air in the system I have one of those yellow radiator funnels that attaches to the radiator and I have ran it with the cone on with the heater blasting 3k rpm engine fully hot fan on while massaging all the hoses. I doubt there is air left.

There is no air getting into the system, I've pressure tested it to spec / a little bit above the spec. 1.3 atm

There are no vacuum leaks I can find. I have pumped the engine up with smoke and watched it pour out of my air intake and nowhere else. Also used some soapy water to look around the manifold and hose endings while the engine is on. Did not see any bubbles.

The butterfly plate is not open too much from when I changed the throttle cable holder. I checked this by pressing the plate on top while the engine is running to see if it closed more and the idle dropped. It did not to an extent of worry, just minimally because I know it is dirty, will clean it later.

I have tried to adjust the base idle with the iacv unplugged. The screw was never in the stock position, so there was no messing it up.
First time unplugging the iacv with the engine running and the idle did not change much but instead sounded weaker with some misfiring. This is when I realized the screw was all the way out and with the screw, all the way closed, then backed off 1 1/2 turns and the iacv unplugged, I can get a base idle of 1000 rpm and it ran smooth no misfires.

This confused me because there are no vacuum leaks and the iacv is off, why would the idle be so high? Being curious I plugged the port to the iacv and the base idle went to 400 rpm. Seems to have solved my problem. I adjusted the base idle to 550 (spec I've read from idle screw reset procedures). Then I pulled the plug on the iacv and way to much air was getting into the system, the rpm raised to 1100rpm and sounded like it was hitting the rev limiter with misfires. Quickly plugged that backup. Decided to see if I could drive and could not go past 1100 rpms as well. So I went and parked the car and it has been sitting there since.

I am unsure what this all means. During all this I ended buying and replacing the iacv with a new one, I knew the old one worked still but people kept telling to do it and I did. Did not do anything. It was not an expensive one but it should still work, right? I did try cleaning the old one too before buying the new one, either way after changing and burping any iacv surges on me.

I will attach some pictures to the post of the engine, but as of now I not sure what to do. Am I writing all this because I need to spend some $$$ on an OEM iacv, or I do need to just go drive it around to relearn the idle? I am pretty sure I do not need to do that because I am a delivery driver and I have used the car for a month while it was idle surging and it never once stopped while driving. Surprised I did not get pulled over for my tags. I did avoid idling tho while I was driving because it was annoying, did I not let it idle enough?

Any thoughts or ideas are welcome I have done a lot thing to the car over the years. I am surprised it is still running. I have tried my best to keep to together but in the end, I guess it is a failed mini-me swap. At one point I did have all the y8 features running with vtec but since then I've needed it to work and has been on the setup listed in the beginning for a couple years running decently. At one point with this setup, it was running fine and was able to pass smog, just can not figure out what I've done this time.

Last minute thoughts:

The ports on the intake manifold I have for the cold air induction system not present on my engine are plugged off with jb weld. No leaks from that.

There is no fast idle valve on the car I can find, not on the intake manifold or the thermostat housing.

Hopefully, this is a good read minus the grammar I missed.
 

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civteck

Respected
Registered VIP
Whats with the tape at the map sensor and dist harness?

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CSIT_Civic

New Member
Whats with the tape at the map sensor and dist harness?

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most of the wires harness had to be separated and moved in order for the plugs to reach the ports when I swapped from a y7 manifold to a y8. The wires are fine they are just rewrapped and moved. The dist is wrapped just to look better, it is a new one because I destroyed the old one..

Thank you for the question!


The throttle cable bracket has a nice bend to it as well. It was the only way I could get the cable to have the proper amount of tension with the y8 intake manifold. It works though, the pedal is smooth to push
 

civteck

Respected
Registered VIP
Well just looked at the pic again, make sure map and tps are not backwards and also the top rear throttle body bolt is loose, could be sucking air there giving a high idle..

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CSIT_Civic

New Member
Well just looked at the pic again, make sure map and tps are not backwards and also the top rear throttle body bolt is loose, could be sucking air there giving a high idle..

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Good spot on that bolt, i can check the two plugs as well, during the swap tho, I made sure to mark them so they did not get mixed up, if it helps the one connected to the map sensor also has the intake air temp sensor on the same pig tail ending. I can verify they are right tho!

With that, it seems most of the vacuum leak is coming from the iavc port itself, even though the bolt is loose


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CSIT_Civic

New Member
Post all CEL codes stored in the ECU. Then reset the ECU to clear the codes, drive the car, and check whether any of the codes return.

Was the donor for the Y8 manifold a 99-00 Civic EX?
Currently It is not throwing any codes but it is hard to drive the car around with no tags! I will attempt to see if I can get any to pop up

The intake manifold may have been from 99-00 because it has ports for the cold air injection system that I plugged up with just weld, the intake manifold part number is P2P IPT-4


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CSIT_Civic

New Member
I am not familiar with the start spray method, is that to look for vacuum leaks? I’ve smoked out the air system, only air escapes from the natural air intake port at the end of the intake tube

For the check engine light, is there a better way to check it, noobish here but don’t you just plug into the obd2 port and get the codes from there with no service pin connected? If so I have no known codes with that method of checking


The p2p ecu is the stock one the car came with, and then y8 manifold was a one from eBay, I just bought one a while a back that was y8 so I could have a horizontal intake port instead of vertical

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CSIT_Civic

New Member
Air would enter (not escape) from the end of the intake tube.

Let the engine idle for 15 minutes with the code reader connected. Without turning off the engine, do any CEL codes appear?

If you use your finger to cover the hole inside the throttle body leading to the IACV while the engine is high idling and surging, does the idle speed drop and the surging stop?

shouldn't air be able to blow past the throttle body into the air intake tube? there are two ports inside the throttle body which the air/smoke might be able to get through, the iacv port and then there is another one, not sure what is it for but I've posted a photo. and circled it.

With idling for 15min I am unable to pull any codes from my code reader, it comes up as clear. I have one a standard code reader from amazon, here is the link: https://www.amazon.com/Autel-MaxiScan-MS300-Diagnostic-Vehicles/dp/B001LHVOVK

for your last question, yes it does, I am able to get 550rpms with the port plugged using a silicone mat, I've read things about applying vacuum to your skin so I hesitated to use my finger. The iacv is new, should not be stuck open right? on a cold start before the radiator fan clicks on and the surging starts the idle will slowly go down from 1700 to 1100 like the iavc is functioning and adjusting the idle.
 

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CSIT_Civic

New Member
Thank you for going through that, here are some answers or my thoughts to your comments, thanks again for the time!

Sounds like the ECU is blown. This often occurs during engine swaps when sensor connectors are mistakenly swapped. You may want to check.

A bad ECU likely explains why you have found no codes thrown.

This could be true, I can add that while I was running it without the IACV plugged in it gave me the code, P1509, only when it was unplugged, I checked the codes frequently during my testing/fiddling. Hooking it back up clears the code. Any other way to test a bad ecu besides swapping?


Install the correct cable and bracket. Hopefully, you did not mess with the throttle stop screw. It is factory set and should never be touched.

Hopefully, I can get the correct one soon, it would be nice. Did not touch the stopping screw, the factory yellow paint mark is intact


How do you know?

I am basing that off of the coolant temp gauge working and the cooling fan cycling when hot, coolant temperature switch is also new because I snapped the plastic terminal connector on the sensor by dropping a 1/2" socket wrench on it...smh lol...


You don't actually know if this is currently true.

true, I do not until I can check it with a steady idle I am quoting it at 12 deg before tdc from last smog results.

Did you mean "suck into my air intake"?

No, I am doing the test with the engine off and blowing smoke into it from the brake booster tube and seeing if it comes out anywhere and it only came out of the air intake.

What? A vacuum leak would not produce bubbles because it sucks air in rather blows air out.

I was thinking it would suck in the water and lower the idle, the sucking process could have also produced bubbles from flowing through a small gap, idk I was just trying something


Given the idle problem, you should have already cleaned the TB.

It could have been cleaned better, to be honest, I will do that.


Unplugging the IACV is NOT done when adjusting the idle speed of a D16Y8 auto.

Good to know, I will keep it plugged in from now on.
 
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CSIT_Civic

New Member
For a running engine, the piston downstroke in the cylinders creates a vacuum that draws/sucks air into the intake manifold via the lower throttle body port for the IACV and via the throttle plate . There's no air escape. The ECU allows some air to enter the lower IACV port and bypass the throttle plate as way to control idle speed.

The upper throttle body port connects to the idle control screw that allows micro-adjustment of the base idle speed. The screw permits a small amount of air to bypass both the throttle plate and IACV for entry directly into the intake manifold.



Did you check for codes during the 15 min while the engine was running? Or did you shut off the engine, and then check for codes?

Yes, while running


Is this^ true when the running engine is either cold or fully warmed up?

Both, checked when cold and after the rad fan cycled

Here's what you should do in this order:
  1. Check whether the TPS is properly calibrated (0.5V at closed throttle and ~4.5V at WOT). Will do
  2. Ohm test the 2-wire ECT sensor below the distributor. Will do
  3. Bleed the cooling system. I have bled the system with a cone multiple times, no more bubbles come out
  4. With the engine fully warmed up, adjust the idle speed using the service manual procedure for an automatic D16Y8.sounds good, have the pdf manual
Then go from there and report your findings.

I will do these and get back,


:shock: Post the "things" you read.

Not sure where I read it, it was a while ago, something to do with slowly sucking the oxygen out of the body through the skin

Should we ban vacuum cleaners?

For body parts lol

:P
 


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