I had just gotten my spark plugs changed about three days ago and the CEL came on shortly thereafter. Got it scanned and the code read P2189 - system too lean @ idle/bank 2. The scanner sighted the likely causes as being either the purge valve solenoid or a problem with the fuel pump. Of course it could be neither of these and I'll get the car looked at this week. Prior to to changing the plugs (and I'm assuming that they did change the wires too), the car had been misfiring badly but the light never came on. After the change, the misfiring has improved considerably, but it still happens at idle (before, they would occur while driving as well). Also; the engine idle speed is higher than usual - near 1,000 rpm - when in park. It's going to be crap-shoot until I get it looked at; but what else could be going on? I drove it to work today and as I had parked and stopped the engine, it made a sound like a hard, sudden stop.

 

When they changed the plugs they may have removed a vacuum hose and forgotten to put it back in place. It could also be that there was a vacuum leak present before that.

There are a bunch of methods to look for vacuum leaks.
1. Listen for a hissing sound and locate the source.
2. Spray carb cleaner around vacuum hoses and near gaskets while the engine idles. When the spraying causes a change in idle you found the location of a vacuum leak.
3. With the engine turned off blow smoke into the intake manifold and see if it comes out somewhere.

 

This is my first instinct as well. They have to remove the intake plenum to change the rear spark plugs on the 3.0 ltr (see pics).
Another possibility is a cracked vaccuum line from unplugging it , then plugging it back in.

For more intake plenum pics: ClickMe

 

Well...I got the car back yesterday and they said that they could not find any problems and did not notice anything unusual while test driving the car...at lest they didn't charge me for their time, but within minutes of driving off their lot I was having the same issues. Eventually, the CEL came back on again with the same lean code. I didn't notice any signs of a vacuum leak, but screw these guys....my wife is taking it to Mazda today. I wonder if they didn't replace the plenum gaskets after they changed the plugs?

 

Another gasket they should have changed is:
Mahle W0133-1807640 Throttle Body Gasket | Auto Parts Warehouse
The throttle body gasket gets black and hard from carbon at the bottom of it.

 

Another reason why it's lean on one side more than the other is because of the design. 1 bank of the engine runs leaner than the other, so with a small leak that side will throw a code first.

BELOW IS FROM: DIY: EGR Modification/Optimization (3.0L V6) - Mazda 6 Forums : Mazda 6 Forum / Mazda Atenza Forum

the Mazda 6s from the factory has a few flaws that may be small and some that can even lead to detrimental damage to the car itself. some of these flaws and/or shortcomings can usually but not always be fixed. But of course the manufactureer wont do it.

Anyway, the design of the Mazda 6s EGR system puts the tube of the EGR directly in the middle of the intake tract. Thats bad business. Basically it blocks the airflow to the cylinders. This compounded with a decently bad design of an Intake Manifold causes 2 issues.

1. one of the 2 cylinder banks will run significantly leaner than the other. How significant are we talking here?
--it has been documented that there is about a 5%-7% difference in fuel trims between the front and rear banks.

******now on a stock motor it probably wont hurt it in the long run. but most of us owners tend to enjoy modding our rides and getting more power. and if this is left stock it could cause engine failure when dealing with power adders such as turbos, superchargers, and nitrous. again 5-7% may not sound like a lot. but that could be the difference of you keeping your 12.2 AFR in one bank......and leaning out to 13.0AFR+ in the other. then boom******

The fix is in the same article, but Mazda won't admit to it. Do this in a different shop.
The guy who made that thread is the biggest Mazda aftermarket Guru guy around: The Great NY -- he has a 3.0 ltr V6 twin turbo charged!

 

Well...it looks like there's light at the end of the tunnel (after Mazda charged us about $150.00 to diagnose the problem). I'll fill you in on the details later, but my wife just called me and said that they have to order this part (air box????) because too much air is entering the custom chamber.....thus the lean fuel issue. That'll be another $300.00!

 

Do you have a custom/aftermarket intake?
Where is the stock old intake?
Air Straightener will be cheap fix: AEM Mass Air Flow Straightener




Clean the MAF? New MAF?

Decisions, Decisions!
This air straightener has to solve someones's problem!

 

OK.....should have just took the car to Mazda in the first place, but here's the deal. The did find that a vacuum hose was disconnected from the air cleaner. Then, we had to replace the #5 coil but wait. Mazda also recommended that they (or maybe I'll do it myself this time) replace the spark plugs because the SOB's who worked on the car the first time used some garbage plugs. I'll also need to replace two other coils (which is probably my fault for having delayed getting a tune up....deferred maintenance is a mother. The code has been cleared and the car runs fine now. We'll get the recommended services done within the next month. In the mean time, I've got to go kill a couple of mechanics.

 

There you go!

" The did find that a vacuum hose was disconnected from the air cleaner."

I'll do a high five with Noggin on this one.

As far as killing mechanics goes i would have a few suggestions.......wait a minute, this is a public forum!