2000 honda civic intake manifold vacuum diagram

Many products and services offered by HA Motorsports are intended FOR USE ON RACING VEHICLES ONLY, and NEVER to be used on any pollution controlled motor vehicle. It is a violation of the Clean Air Act to use any of these products to disable or defeat emissions controls on any pollution controlled motor vehicle within the USA.

Junior Member

Thread Starter

Join Date: Dec 2009

Posts: 6

I recently have the code P0420 Catalyst System Efficiency Below Threshold (Bank 1) keep poping up every 80km or so after I reset. My cat was replaced 1 year ago, so I think that should not be the problem. The code P0505 Idle control malfunction also pop up sometimes, but a lot less.
I replaced the sparker plugs to the OEM ones and the problem still persist.
So I assume that is the oxygen sensors because I think for P0420 is usually either cat or oxygen sensors. I replaced them with Bosch oxygen sensors direct fit.
I have not been driving enough to see if the code will pop up again. However, I noticed that the accelerating is sluggish. So I checked the timing. It is at 16 deg adv, so it is good.
I then check the IACV. When I unpluged it, the rpm does not drop that much.
It stays at around 750 to 850 rpm. ( I am driving manual, it is suppose to be 450 + - 50 rpm).
I removed the duct from air filter and blocked the port inside TB that connect to the IACV, I feel some suckion and the rpm dropped a bit further, but not too much. Is there something wrong with the IACV? I think it is suppose to be shut when unplugged. There should not be any suction. The idle adjusting screw on TB was almost closed, but the rpm is still at around 750 to 850 rpm.
I then blocked the whole intake on TB and the rpm still pretty much the same, only drop a little bit.

I then connect everything back and reset the ECU. After that, I unplug the ducts from intake manifold one by one and block the hole on the intake manifold. The rpm does not change much.

I find 4 ducts on the intake manifold.
- to PCV valve
- to purge control solenoid valve
- to oil pressure regulator
- to cruise control. (I think, but I am not sure. It is the biggest duct that is on the rear driver side of the intake manifold.

I read somewhere that there should have a duct to the brake. But I do not see this duct. Did I miss this one?

I also sprayed TB cleaner on the connection between intake manifold and engine, between IACV and TB and TB to intake manifold, but no change in rpm.

I think it can be 2 problems.
- IACV leaking
- intake manifold leaking

Anyone with any good suggestion?
I have a gauage that can measure the pressure on intake manifold, what should the normal pressure be? I have not try that yet.

I also checked with my ODBII the MAP reading is around 7.4 Hg something like that. Is that normal?

Last edited by skyclimber; 01-20-2012 at 05:33 AM.

Junior Member

Thread Starter

Join Date: Dec 2009

Posts: 6

Today, I did some more testing again.
I blocked all the nozzle to the intake manifold, blocked the TB, unplugged IACV conntector, but the engine is still running at 750rpm.

I still hear some air leaking sounds from the intake air duct.
There's the air temperature sensor and 2 ducts coming from the engine.
One duct, there is air coming out from engine, so that cannot be it.
The other one, on the contrary, is sucking air.
So I removed the tube from the intake air duct and blocked it, the engine died right away.

Since I blocked all the air entrance to the intake manifold, the only place air that can go in is the TB screw and this tube.

From the diagram on the hood, I assume this is where the FIAC valve is.
I have no idea what is the FIAC valve and never heard of it. I also cannot find much information about this.
Can anyone tell me what is this, and should it suck air?
I attached some pictures regarding this.

Join Date: Jun 2007

Posts: 10,023

Your second picture is the FITV (Fast Idle Thermal Valve) mounted on the thermostat. It is supposed to close fully when the engine is warm.

Junior Member

Thread Starter

Join Date: Dec 2009

Posts: 6

I did a lot more research and find that the FIAC valve only exist in the 99-00 models!
It is same as FITV. Since it is wide open when the car is warm, something is wrong with the valve!
I ordered a new part from Honda, and it costed my $157.03!!!
I will try to clean it and see if it works. If so, I am going to refund my new valve.
Thanks for the input.

Join Date: Jun 2007

Posts: 10,023

You could just block it off. It only does anything when the temperature is below 60 F, even then the car should run without it.

Junior Member

Thread Starter

Join Date: Dec 2009

Posts: 6

You are right.
May be I just block it off.
How is this going to affect the fast idle before the car warm up?

Thread

Thread Starter

Forum

Last Post

sub310

Inside and Out

3

04-09-2012 01:59 AM

skyclimber

Mechanical Problems & Technical Chat

1

01-01-2010 07:11 AM

dustinwithanx

Mechanical Problems & Technical Chat

0

11-21-2009 09:29 PM

texasmade

Engine & Internal

6

02-03-2009 05:59 AM

xonic

Mechanical Problems & Technical Chat

1

05-26-2005 04:58 PM

2000, air, civic, d16y8, diagram, dies, honda, iac, intake, leak, line, o2, sensor, starts, vac, vacuum leak