That is a vaccuum line. it may be your problem. it has a 1 way check valve (white thing).
It actually plugs in to the stock air box on left front side. Eventually it goes beside the air box and helps controls the Extra Air Flapper on the side of the Air Box and it also has an electrical connection by flapper (green solenoid thing).
Good Find. I would leave it plugged in with stock box.
Normally, with an aftermarket intake that line gets plugged.

 

Well, it didn't fix it. Its running better but the light is still on (it went off then went on again). There is a SLIGHT sound of what sounds like an exhaust leak when I'm turning right and only when turning right...thinking maybe a bad engine mount?

Going to get it looked at again with the same guy. Also might try to see if it could possibly be a fuel injector or fuel pump. I'm thinking it could be the fuel pressure.

 

Take a good close look at the exhaust Flex pipe area as well (there are 2 of them on the V6)----I've had mine changed twice. The stock rear lower engine mount is not great. Try AWR: All Parts - Engine Mounts - Mazda6 - AWR Racing Store
there are slightly different ones depending on your tranny. Make sure to contact them first before ordering.

 

There was only one code now, 174.....

he said it wasn't an exhaust leak but what i was hearing was from the EGR.

He used his scanner, everything was running fine in real time and everything seemed to be working ok. The LongFT1 and LongFT2 were about 12.
He's thinking it may be an O2 Sensor starting to go bad. But kind of scratching looking for a solution.

 

He suggested that I drive it around a bit and wait for the light to come on so he can look at the freeze frame data and replicate it. Also suggested checking if there were any recalls or service bulleltins at the dealership. He pulled up a few of them. There were a few in 2005 that had to do with the pump control circuit failure .


and a 02 Evaporatative Emissions system leak monitoring failure (3205G recall)

and a PCM/TCM reprogramming for I/M Failure.

 

Any software updates for the computer are free from the dealership. I have gone in the past to check the computer for updates. If there are, no charge, if no updates, you pay.

 

He didn't check but I do think I have a broken engine mount and I do think it is giving an exhaust leak...
yesterday I noticed the exhaust smell in the cabin and when I do go over bumps its still a thump. Just my hunch...he only had time go read the codes the other day.

 

The OEM wishbone engine mount on the Mazda 6s has been known to be a weak link. One of the biggest issues is the OEM rubber which will tear with any kind of spirited driving. Seriously consider previous post AWR.
I think i'll be buying one as well.

 

they checked the engine mounts, they said they were weak but not causing the problem. They said the noise I'm hearing when turning and on cold start ups is coming from the Serpentine Belt tensioner. Thoughts?
Serpentine Belt Tensioner at 1A Auto

I'll try to take a video tomorrow AM...

 

I've been re-reading your thread and on other forum. You have had misfires and lean codes. You have 105,000 miles on it.
You have changed 3 ignition coils and no spark plugs (although idiot flipper on other forum thought you changed them all and both---he skims alot but he is generally good).
I would have changed all the coils and all the spark plugs (with that mileage). What idiot changes coils without spark plugs is beyond me. One of the coils may have caused a misfire, but the spark plug associated with it might not be up to snuff and clogged. However, these causing a lean code is a puzzle.
You said you had a exhaust leak on your pre-cat?----did this get fixed? I am not as confident as you in your exhaust being fixed (welding an old pre-cat). However, with that mileage especially, a bad pre-cat can and does cause a mis-fire (Mazda recommends them changed @ 100,000 miles but they should last longer with proper spark). Misfires will screw up your pre-cats: Reasons For A Converter Failure . What is your current cel code? I believe you have changed one O2 sensor---- hopefully it was the first one on the exhaust stream.
The EGR is not suppose to kick in @ idle, however it does over 1,200 rpm or so. If you are hearing something there, get some one to take it apart and clean it (again it should be cleaned due to mileage).
Your tensioner could be shot at your mileage. If you replace the tensioner, change the belt.
You have got a lot of things going on with high mileage. I don't really know what your solution is, but a few things need tending. Did you check your accordian tube on intake for cracks? A bad brake booster will cause a lean code (it leaks internally and is hard to detect---you have to actually wait until once or twice you lose power brakes).
When changing plugs or coils on rear bank closest to firewall, intake plenum must be removed, I hope he changed the 6 green intake plenum seals--see pic (like this: OES Genuine W0133-1639826 Intake Plenum Gasket | Auto Parts Warehouse )along with the rubber seal between the throttle body and intake manifold (like this: Mahle W0133-1807640 Throttle Body Gasket | Auto Parts Warehouse .