I just bought a trade in from a dealership that i work at (2000, lx, 1.6, 117k) and so far its been running fairly well. It idles kind of rough at about 700-500 rpms and a check engine light came on about a week ago and its a p0420 or 30 (Catalyst System Efficiency Below Threshold) and I'm trying to fix the problem. I was going to just replace the cat but then i found out about the pre-cat and found out how much it was to replace that and I have had a couple different people tell me that the cat isnt necesarily the problem. I replaced the spark plugs with basic ngk's gapped at .044 and replaced the wires and it still idles rough but i havent cleared the code yet. We opened the hood and there seems to be a slight clicking noise coming from a little sensor thing (looks like some kind of vacuum sensor) thats connected close to the top of the throttle body and i dont know if that noise is normal or not and i have no clue what this thing is. It has two hoses going into the bottom of it and a electronic plug in the top. One hose goes to the throttle body and the other goes to a black canister near the front passenger wheel well. I've thought about replacing the ignition coils or testing them if possible and also the o2 sensors. I really just need some kind of help on where i should start.
CEL, rough idle
- Thread starter ss1204
- Start date
forgot about exhaust
I forgot to add that when I took apart the interior to replace the carpet that i noticed when i was driving around and the rpms went above 3500 that i heard a sound that sounded exactly like a turbo(high pitched whine) coming from the back passenger area. When I reinstalled the back seat i stopped hearing the noise which im pretty sure the seats just deadening it out. I looked for a leak in that area of the exhaust but i couldnt find anything. I was also told that an exhaust leak could cause that code to pop up.
I forgot to add that when I took apart the interior to replace the carpet that i noticed when i was driving around and the rpms went above 3500 that i heard a sound that sounded exactly like a turbo(high pitched whine) coming from the back passenger area. When I reinstalled the back seat i stopped hearing the noise which im pretty sure the seats just deadening it out. I looked for a leak in that area of the exhaust but i couldnt find anything. I was also told that an exhaust leak could cause that code to pop up.
I'll PM later
You Wrote " We opened the hood and there seems to be a slight clicking noise coming from a little sensor thing (looks like some kind of vacuum sensor) thats connected close to the top of the throttle body and i dont know if that noise is normal or not and i have no clue what this thing is."
Please reference my earlier posts. I had a very very bad rough idle problem and I have mitigated nearly 90% of it by cleaning th EGR vavle. However, just the other day (and this morning) I have a slightly rough idle (500-600) at times with the occational engine light. I also here that clicking noise that you are talking about and I have no idea if that is normal. It is coming from that same sensor thing on top of the air intake tube or the throlltle body ( I cannot tell).
If you figure anything out please advise.
You Wrote " We opened the hood and there seems to be a slight clicking noise coming from a little sensor thing (looks like some kind of vacuum sensor) thats connected close to the top of the throttle body and i dont know if that noise is normal or not and i have no clue what this thing is."
Please reference my earlier posts. I had a very very bad rough idle problem and I have mitigated nearly 90% of it by cleaning th EGR vavle. However, just the other day (and this morning) I have a slightly rough idle (500-600) at times with the occational engine light. I also here that clicking noise that you are talking about and I have no idea if that is normal. It is coming from that same sensor thing on top of the air intake tube or the throlltle body ( I cannot tell).
If you figure anything out please advise.
the 1.6 does not have an EGR 
the first spot i would check would be all of the points where the exhaust pipes meet up. make sure everything is tight. you may be able to see/feel the exhaust gasses coming out at a gap/crack. if you do it on a cooler day it makes steam
the first spot i would check would be all of the points where the exhaust pipes meet up. make sure everything is tight. you may be able to see/feel the exhaust gasses coming out at a gap/crack. if you do it on a cooler day it makes steam
I have the same problem and have done all he above. Cleaned EGR, replaced spark plugs, replaced full exhaust system (not header) and patched a header leak. I have done new plugs and wires, installed a new CAI.
I JUST got a engine code which I was told means that my idle air control valve is going bad. After reading up a bit on what the IAC does, I think its VERY possible this is the root of all our problems. The idle control valve is a solenoid operated valve that lets air by-pass the closed (at idle) throttle plate, thus allowing the car to idle. Idle speed is adjusted by the computer by opening and closing the valve. If that is gummed up, then all the crap in the world will not work unil that is replaced or cleaned. Now Mazda sells a new one for, brace yourself, $600!!!! I am sure we can get cheaper, but for now I want to know if we can just clean this bad boy. I have read that it collects carbon buildup and that causes it to not open properly and will make your idle look like its "searching" for the proper speed. I also noticed a MUCH increased dip in rpms when the radiator fan comes on. Everytime it starts my rpms shot down to almost stall the car.
So now guys, we have our demon and just need to know how to kill it.
I JUST got a engine code which I was told means that my idle air control valve is going bad. After reading up a bit on what the IAC does, I think its VERY possible this is the root of all our problems. The idle control valve is a solenoid operated valve that lets air by-pass the closed (at idle) throttle plate, thus allowing the car to idle. Idle speed is adjusted by the computer by opening and closing the valve. If that is gummed up, then all the crap in the world will not work unil that is replaced or cleaned. Now Mazda sells a new one for, brace yourself, $600!!!! I am sure we can get cheaper, but for now I want to know if we can just clean this bad boy. I have read that it collects carbon buildup and that causes it to not open properly and will make your idle look like its "searching" for the proper speed. I also noticed a MUCH increased dip in rpms when the radiator fan comes on. Everytime it starts my rpms shot down to almost stall the car.
So now guys, we have our demon and just need to know how to kill it.
