A pressure test bya pro will give you the answer.

 

If you havent been told to do so yet.. spray brake clean.. or propane around the intake manifold..

These 3.0's are NOTORIOUS for the gaskets going bad.. Warning though.. the fumes produced after the propane or brake clean goes into the engine is highly noxious

 

Mahle W0133-1807640 Throttle Body Gasket | Auto Parts Warehouse

This throttle body gasket gets hard @ the bottom. Change if never changed especially with 105,000 miles and removed already.

OES Genuine W0133-1639826 Intake Plenum Gasket | Auto Parts Warehouse

These 6 intake plenum rubber gasket seals get hard also after a while (cracking).

I've already changed mine and I have less than 1/2 your mileage.

 

I am pretty sure the intake plenum gasket had been changed. I will have to double check. I've sprayed with carb cleaner, didn't find any leaks. I'll try again.

 

put in a bottle of redline fuel treatment. not sure if it'll do anything, doubt it.

 

There is six of those gaskets under there... one per cylinder.. Those are the exact gaskets that goes bad

 

ok. I'll get that checked next. along with fuel pressure and the EGR. I sprayed with carb cleaner last night to check for vacuum leaks, didn't hear anything that would indicate a leak.

Im going in Thursday AM to get the serpentine tensioner changed, I'll have them look at those.

 

Are those under the engine cover? I recall the mechanic saying to replace them since they looked like they cracked and there was some oil there? Would that give me a lean condition?

Is it costly for them to do? He said the rear ones were harder to get to.

 

That's an oil leak.

See post 63 for link to see engine intake plenum seals. They are under the Black Intake Plenum (first thing that comes off -- your EGR valve also attaches to it. See pic from underneath (6 green seals).
OES Genuine W0133-1639826 Intake Plenum Gasket | Auto Parts Warehouse

I'm really racking up the post count with all these double posts on this thread. Please re-read everything.

 

OK, this is weird, ever since Tuesday the light has been off. When I went to get my serpentine tensioner done, I had them reset the code (both same lean codes).

Hasn't come on since. The light had previously gone on and off, but usually comes on within 3 drive cycles, and I've filled up since then and driven for several days and many drive cycles. This is also before I fixed the engine mount.

Coincidentally I had started using chevron too...and I had run that redline fuel system cleaner about 2 weeks prior.

1. The chevron gas is better for my car? I did use 89 octane on the last fillup.
2. that redline fuel system cleaner cleaned something causing my car running lean
3. serpentine belt tensioner replacement did something to fix an issue? (don't know how, since its not connected to anything that would do this?)
4. When installing the tensioner they perhaps fixed up an air leak when putting everything back together
5. completely random occurrence.

just waiting for the light to come back on eventually. hopefully it doesn't but it makes me wonder. also knocking on wood that it doesn't, was waiting a few days of monitoring before i posted this.