CSIT_Civic

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.

Edit:

I took the pictures all upright right sure how to rotate them....
If you open them in a new tab they appear correct