skyclimber

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?

Former User

Sounds like you need a full tune up.

By the way, an engine that is running rich (e.g., due to misfiring) can kill a new cat very quickly.

skyclimber

What should be done in a full tune up?
The sparker plugs, air filter are 1 month old.
oil filter is one year old.
Timing checked with timing light and is on the red mark.
idle is what I am having problem with because the rpm cannot be lowered.

The engine might be running rich, and misfired? Is it due to the injectors? Timing? Or idle air control?
If the engine misfire, when I block the TB, is the rpm going to stay pretty much the same?
The car is running fine for now, except may be I will have to reset the MIL every other 80km. If I run my car like this, is it going ot hurt my engine?

skyclimber

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.

skyclimber

I found out more about the FIAC valve. It is like the FITV. #24



Here is a thread with more details.
https://honda-tech.com/forums/honda-civic-del-sol-1992-2000-1/00-civic-where-does-hose-fuel-injection-air-fia-control-system-connect-2654884/

skyclimber

Thanks RonJ for your post 2 years ago.
It really helps.