Honda Civic / Del Sol (1992 - 2000) EG/EH/EJ/EK/EM1 Discussion

3 Wire IAC Harness to 2 Wire IAC?

 
Old 03-13-2019, 04:37 PM
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Default 3 Wire IAC Harness to 2 Wire IAC?

Hey guys,
So I'm in a bit of a pickle. I finally was able to get my first Honda on Monday, but it came with a lot of it's own weird problems due to a half ***'d swap. So heres what I have.

97 Honda Civic DX
D15B2
P2E ECU

So here's the problem. The IAC that's on this manifold is a 2 wire IAC with the stock OBD2A harness. I have a code 14 and of course, my IAC doesn't work. Looks like the previous owner tried hooking it up, but it's not right. No idea what wires he had hooked up to it and it's been raining for a good while now so dont have much time to check FOR SURE. From what I see (if this is the stock wires) He has a Red/Blue and a White/Green wire running to the 2 wire IAC, which according to the pin out, is FAR from right. But maybe thats just spare wire he used. I will unwrap the harness this weekend when it clears up and check for sure. I've done so much research on this topic but everyone shows how to do a 3 wire to 2 wire swap when you switch to a OBD1 ecu. That's not an option right now. So from my understanding, On the 2 wire IAC, the Green/Black is supposed to be a constant positive and the Black wire is supposed to be an ecu controlled ground. So here's the thing, from what I read, the 3 wire has a fluctuating positive and negative. So could I run a constant positive to the Green/Black on the 2 wire connector, and then run the Orange wire on the harness to the black wire on the 2 wire connector? According to the schematic the Orange wire is the IAC negative for the stock harness. Or is the possibility of running a 2 wire IAC on the stock OBD2A ecu not possible due to there not being a way for the ECU to know how to control this? I've been researching day and night and I just want my car to run right man... I can't sleep without fixing this.

Just to clarify a little bit more on the main problem I'm having, the idle jumps up and down on a cold start. When it gets a little heat into it, it idles pretty smoothly, or good enough that it doesn't bother me. When I'm driving, If I'm between like 1,750 RPM to 2,250 RPM (round about there) it stutters REALLY badly on partial throttle. It's fine if it's higher than that and fine if it's lower than that. From my understanding this is due to the IAC, though it is also throwing a crankshaft position sensor fluctuation code (code 54), which is possibly the reason, but from my research it's the IAC causing the bad stutter.

I just want the car to drive normally until I can do it RIGHT, with an OBD1 ecu and an actual OBD1 wire harness. I absolutely love this car and I will make it SO CLEAN. I just need to get by for now until I can recoup from the purchase. So please guys, any help in at least making the car drive smoothly without that stutter would be greatly appreciated. Whether that may just be deleting the IAC, or finding a way to make it work, it doesn't matter. I know this community has some amazing members in it and I'm glad to be a part of the Honda family finally!
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Old 03-13-2019, 05:35 PM
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Default Re: 3 Wire IAC Harness to 2 Wire IAC?

The circuitry inside the ECU is different for 3 wire valve vs. 2 wire. You cannot connect a 2 wire valve to 3 wire ECU or vise versa.

Which brings us to the fact that all non-VTEC OBDII ECU's are made for 3 wire IACV. The only OBDII Civic that uses a 2-wire valve is the manual EX, the ECU for which also expects to find a VTEC engine.

The first thing to do with any car that was improperly swapped by someone else would be to not buy it. Well OK if you do happen to have such a car you need to inventory all the parts that are on it and find out what does not match.

You're getting a CKF code because OBD1 engines have no CKF mounted. There are a couple of ways to work around that.

Installing an OBD1 system in a car that was originally OBDII will not be legal in California and likely some other places that have strict smog laws.
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Old 03-13-2019, 05:39 PM
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Default Re: 3 Wire IAC Harness to 2 Wire IAC?

Originally Posted by mk378 View Post
The circuitry inside the ECU is different for 3 wire valve vs. 2 wire. You cannot connect a 2 wire valve to 3 wire ECU or vise versa.

Which brings us to the fact that all non-VTEC OBDII ECU's are made for 3 wire IACV. The only OBDII Civic that uses a 2-wire valve is the manual EX, the ECU for which also expects to find a VTEC engine.

The first thing to do with any car that was improperly swapped by someone else would be to not buy it. Well OK if you do happen to have such a car you need to inventory all the parts that are on it and find out what does not match.
Thank you so much bud! Thats exactly what I was looking for! Guess in gonna have to swap manifolds, which I'm not too mad about lol. For now I'll just delete it and hope it runs smoothly at that RPM range. I heard the idle will be a little high, but I can live with that for now!
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Old 03-13-2019, 05:45 PM
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Default Re: 3 Wire IAC Harness to 2 Wire IAC?

Any OBDIIa intake other than manual EX or either HX will solve your problem, it will have the 3 wire valve. The auto EX is preferable because it has better flow.

A 2 wire IACV that is unplugged is functionally the same as not having one at all. And "IACV delete" will never run well. There's a reason Honda bought one for every car in the first place.
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Old 03-13-2019, 06:05 PM
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Default Re: 3 Wire IAC Harness to 2 Wire IAC?

Originally Posted by mk378 View Post
Any OBDIIa intake other than manual EX or either HX will solve your problem, it will have the 3 wire valve. The auto EX is preferable because it has better flow.

A 2 wire IACV that is unplugged is functionally the same as not having one at all. And "IACV delete" will never run well. There's a reason Honda bought one for every car in the first place.
Ok thanks! Maybe I'll see if I can go to a pick and pull this weekend!
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Old 03-13-2019, 06:17 PM
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Default Re: 3 Wire IAC Harness to 2 Wire IAC?

Originally Posted by mk378 View Post
The circuitry inside the ECU is different for 3 wire valve vs. 2 wire. You cannot connect a 2 wire valve to 3 wire ECU or vise versa.

Which brings us to the fact that all non-VTEC OBDII ECU's are made for 3 wire IACV. The only OBDII Civic that uses a 2-wire valve is the manual EX, the ECU for which also expects to find a VTEC engine.

The first thing to do with any car that was improperly swapped by someone else would be to not buy it. Well OK if you do happen to have such a car you need to inventory all the parts that are on it and find out what does not match.

You're getting a CKF code because OBD1 engines have no CKF mounted. There are a couple of ways to work around that.

Installing an OBD1 system in a car that was originally OBDII will not be legal in California and likely some other places that have strict smog laws.
Oh, also, do you know how to get rid of the CKF code? I'd like to not have a check engine light xD.
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Old 03-13-2019, 06:23 PM
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Default Re: 3 Wire IAC Harness to 2 Wire IAC?

Originally Posted by Chaosgrunt View Post
Oh, also, do you know how to get rid of the CKF code? I'd like to not have a check engine light xD.
NVM, Found it! \o/ I'm so excited!
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