I know there are already thousands of threads on the fluctuating idle issue, but I can't seem to fix it. I have tried replacing the TPS, IACV, and just out of desperation, the MAP sensor too. I checked all vacuum hoses for leaks but everything is fine. This has been happening since I've got my 2000 EX working, as I bought it with an auto transmission and a seized engine, so I did a complete engine rebuild and transmission swap to manual. I was expecting the IACV on the car with the manual transmission to have the two prong plug, but it was a three prong. I don't know if that could be the issue or what. I'm really contemplating replacing the TB gasket and intake manifold gasket even though they are both brand new because I really can't think of anything else. Someone smarter please help me.

 

Did you thoroughly bleed the cooling system?

CEL codes?

Are you running the engine on an OBD2B P2P ECU for a manual transmission, which requires the 2-wire IACV?

 

I have bled the coolant, forgot to mention that.

And no, when I bought the car I also bought a CX with a manual transmission but it had been T-boned, I took the D16y7 engine out of it along with the transmission, rebuilt the engine because it was about to fail too (bought it from the same people as the EX, guess they didnt know oil changes existed lol) and swapped the engine into the EX. I'm using the P2E ecu from that car.

 

so what throttle body are you using?

Are you using the y8 intake manifold on the y7 motor?

What engine is in the car from what year
What cylinder head
what intake manifold
What year is the ecu in the car?
what model idle air control valve are you using

Your last sentence confused me, that you swapped the engine from the dx into your ex? You are using the ex ecu to run the dx motor?

 

And no you don't have a typical idle issue thread

The issue is that in 1998 honda changed the ecu and some of the sensors to run obd2b software. You're trying to use the 1996-1997 sensors using the wrong ecu and engine harness.

 

What CEL codes are thrown?

Do this test:

1. Remove air intake system.
2. While engine has the hunting idle problem, use you finger to cover IACV hole inside throttle body.
3. Does the hunting idle smooth out?

 

I have no idea what you're talking about, chrysler. 96-98 Civic sensors are fully compatible with each other.

 

Also I am using sensors and a harness from a 2000 car, with an ecu from 97', but like muellersfan said, they should be fully compatible (did hours of research before I just tried hooking everything up and starting the car).

 

I swapped the dx engine and transmission into the ex, and I am using the dx ecu so the car doesn't freak out because of the absence of the V-TEC and the automatic transmission.

 

The 2000 Civic engine harness (OBD2B) will require a conversion harness to connect with the 1997 ECU (OBD2A).

 

I thought you had no idea what I was talking about, Mueller.

 

Re-read your post. I think you made a typo because I know that you know better.

 

I made a mistake fellas, and honestly this just makes it more complicated, it turns out the Car I took the engine, transmission, and ECU out of was a 2000 Civic DX, not a CX. So it is using the OBD2B harness with OBD2B sensors and an ECU that is looking for OBD2B signals. So that can't be the problem. I looked up a fog machine to the throttle body over the weekend and found out I had a leak in my throttle body gasket and Intake manifold gasket (don't trust FEL-PRO, waste of money), so I threw some brand new OEM gaskets on, rebled the coolant, still idle surging. While I was bleeding the coolant though it started out fluctuating between 1000 and 2000 RPM's, but after the coolant his 96 degrees Cel. (where the radiator fan turns on), it started fluttering around 1500 RPM which made me think it was a problem with the TPS. Turned the car to accessory and spliced the TPS wire to see if it was working properly and it was at the correct voltage when no throttle and 4.5 V at full. (I can't remember what it is supposed to be at no throttle off the top of my head right now, either 0.5 V or 0.05 V). Any Ideas?

 

2000 D16Y7 engine and P2E ECU swapped into a 2000 Civic EX with a manual transmission swap. Is this correct? If so, you must use 3-wire IACV.

The TPS output voltage should be very close to 0.5V with the throttle plate fully closed.

 

Yup that's exactly what I have and I do have the 3-wire IACV. And yeah I got it to 0.5V with throttle closed. Sorry for taking so long to reply, internet went out for a few days.

 

Try the test I mentioned.

 

Okay so it has been a few months, and to be completely honest I had completely forgotten about this thread until just now.

Well, it did take me about another hair-pulling, wrench-throwing, cussing-out-everything-from-the-sky-to-my-trash-can month before I finally figured out the problem, and I discovered the solution completely by accident. I just want to post this reply in case anyone stumbles upon this thread in the future so maybe it will help them before they lose their sanity like I did.

Air Injection (noun)
/er/ /inˈjekSH(ə)n/
The most awful thing ever invented. The only reason for any drop of hatred in my soul.
"**** air injection"
Synonyms: ****, *******, ******* piece of ****

In the 1999 and 2000 model years, the D16Y8 engine head was equipped with an air injection system. This system consisted of holes on the intake manifold and one hole on the head for air to pass through. When a D16Y8 intake manifold from the 1999-2000 model years is paired with a 1999-2000 D16Y8 head, there are no problems. When the same intake manifold is paired with literally any other head, you get a massive vacuum leak. If you have said vacuum leak and you are reading this now, then CONGRADULATIONS you have the hard part over with, hopefully it didn't take you as long as it took me. Only thing left to do for you is to grab some JB Weld and plug those sons of ******* right up and badda-bing badda-boom, you have a normally idling car!! If you are wondering what holes I am referring to, they are itsy bitsy little holes about each intake port on the intake manifold. I have included a picture so there is absolutely no confusion as to what you are supposed to be plugging.

 

Glad you found the fix.

​​​​​​​Most people would have identified the problem immediately had you mentioned that a 99-00 Civic EX IM was installed on the D16Y7 engine.