Hello all,

Recently I have been doing a D16Y8 head swap on my 1996 Civic CX.

Here is a rundown of what has been done and what the problem is;

D16Y8 Head
D16Y8 Intake Manifold (Auto)
D16Y7 Throttle Body (to keep the 3 wire IACV)
P2P ECU
IACV re-pinned at ECU (Moved A14 to A12 and removed A13)
Knock sensor installed and pinned
VTEC installed and pinned

I **think** we have all Vacuum lines ran correctly.

Here is the problem(s);

No CEL codes when running, except where noted below.

Car starts up and builds to 5000 RPM, then slowly makes it way down to 1500 RPM and then shoots up to 2500 RPM...back down to 1500, up to 2500, etc etc. So basically we have an idle surge problem.

At first we were using a 99-00 IM, that had air injection ports on it and we thought that was giving us a vacuum leak. We picked up a 96-98 Intake Manifold and after switching it out get the same result.

Used carb spray to try to spot a vacuum leak and couldn't find anywhere that the spray would cause the car to rev up.

Next we unplugged the plug from the IACV sensor and now when we start, it goes to 1500 RPM and bounces to 1600, back to 1500, etc, etc. Obviously this throws a CEL, but that would seem to rule out a vacuum leak being our problem? I am assuming if we had a leak that unplugging the sensor plug would still have the car surging, no?

We also tried taking the ECU pinouts back to stock configuration with the D16Y7 ECU and still get the huge idle surging.

Any ideas on what might be the source of our problem?

Thanks!

 

try cleaning your fast idle valve. Its what control your idle untill engine warm up. If rpm is still high at operating temp. than u need to go back in and adjust your idle screw.

 

hmm, I thought you were supposed to switch to a 2-wire iacv when doing this swap?

I may be wrong though.

 

Is your civic Auto?

If its not this is your problem.

D16Y8 Intake Manifold (Auto)

You can't use a auto Intake Manifold on a manual car.

I had a buddy who had a 97 hatch with a Full Y8 motor but a Auto Manifold and it was always running messed up and reving up and down.

Find another good manual Manifold and you should fix your problem man.

 

yeh, I'm pretty sure he is correct, because the manual uses a 2-wire iacv which is what that ecu needs, otherwise it runs like ***. (which is what you are experiencing now)

 

Agreed, this is probably the issue here.

Thus you can avoid the re-pinning when using a y7 longblock on y8 manifolds/etc as long as the vehicle is an auto--doesn't help you much in this case though...

 

Here is a little update.

We ended up trying to ground the orange wire from the IACV and on start the RPMs increase like it normally should (instead of spiking to 5000 before coming down).

No CELs or idle surge.

We let the car warm up for 10 mins and it was still running normal. Decided to take it for a test drive, and once we got out on the road and the thermostat opened up, the surge came back.

Let the car cool down and repeated with the same thing happening (running fine until warmed up).

Any thoughts?

 

Is th coolant topped off in the radiator? Bleed the cooling system. You likely have air trapped in the system.

 

Thanks for all the input so far. Will be checking the coolant situation shortly.

 

I have a spare IM if you need one from my manual 99 Civic (d16y8). Send me a PM if you are interested. GL with the set up!

 

Update:

Bled the coolant lines and still have the idle surging.

Could the D16Y7 injectors be causing a bad air/fuel mix? The D16Y8 injectors that were on the fuel rail I picked up were missing pieces, so we used the D16Y7's. Don't want to drop another $300-350 on new injectors if it won't be the fix.

Thoughts?

 

Hey I had the same problem when i did my head swap. what I did was I got the y7 throttle body, or just one with out the iacv on bottom the throttle body and used a y8 tb gasket. Somehow the 3wire iacv leaks air when its not working.

 

Again as someone else already asked, is the car an automatic or a manual? Answer the question, we can't really tell you anything without that info.

If its an automatic repin you IACV connections back to stock at the ECU. Otherwise get a manual Y8 throttle body and intake manifold and cut and splice on a 2 wire IACV plug.

 

The car is manual. I have seen a lot of posts where people say they used an automatic intake manifold on manual setup with stock D16Y7 TB/IACV. I guess that is not an option?

 

im doin this in the next week with my cx hatchback ill post when I can. - A

 

Correct, it doesn't work. Use a manual throttle body and intake manifold.

 

did you use a y7 throttle body gasket?

 

The part #'s at the auto stores are the same for the D16Y7 and D16Y8. The only difference is that there are part numbers for automatic and manual that are different.

We are currently using the manual version. Looking at the pictures of the 2, the auto version seems to be smaller.

 

Bump for update.

After sitting on this for a couple weeks we decided to take everything back to stock (other than the cylinder head) to see if it runs normally. Reason being is that I ended up getting a newer car and don't want to dump more cash into this problem before I sell it. The car ran fine with the stock setup, so I figured it would be better just to put it back to stock.

We didn't think that the D16Y8 head would cause a problem, so we left it in considering it is rebuilt.

Took EVERYTHING back to stock configuration and we have the same exact problem. Idle surge with the IACV hooked up and with it unplugged the surge goes away and it idles rough at 1000 RPM's and throws a CEL.

Any ideas?

Thanks.

 

hmm, did you check for any vacuum leaks? You might have forgotten to plug up a vacuum hose or it could just be leaking at the intake manifold gasket or the TB gasket. You could also try taking the iacv off and cleaning it.

 

my civic does this sometimes. i turn on the a/c and it goes away. when i first installed the motor it did this i installed a new intake and it fixed the prob.

 

Tried cleaning the IACV. Surge didn't go away. The IACV was working perfectly fine before the swap.

Could the D16Y8 head be causing the surge?

Does unplugging the IACV and the surge goes from a 1500 RPM bounce (2000-3500 RPMs) to a higher than normal small idle bounce (1000-1100 RPMs) mean that the IACV is bad? or that there is a vacuum leak somewhere else?

We re-checked all the vaccum lines and cant find a leak. If hoses are crossed somewhere, would that cause a leak?

Thanks.