Lean running condition
 

I am getting persistent 1128 and 1130 codes. The duramteric shows fuel trims (FRA, RCAT) at the max, 4.5+. Also, the MAF flow is as 9-10 kg/min, where before, it was around 13.5 (spec is 15 +/- 1.5). I've installed three different MAFs and they are all around 10, so I'm ruling out the MAF as the culprit.

I think its pretty clear I have a vacuum leak. I've sprayed carb cleaner on most of the vacuum lines and connections behind the MAF, but I haven't been able to detect a vacuum leak.

Is it possible that a failed AOS will cause a vacuum leak and 1128 and 1130 codes? If so, can I test the AOS by disconnecting the AOS connector at the throttle body and plug everything up, then if the MAF flow readings go back to normal, the AOS is the cause of the vacuum leak?

Another code I am getting is a failed evap valve. Will a bad evap valve cause a vacuum leak?

This is driving me crazy.

Most definitely..................

Can I check if its the evap valve by pinching off the vacuum hose to the motor and seeing if the MAF values go up?

Oh, and will a failing AOS also cause a vacuum leak?

A failing AOS diverts vacuum to where it should not be; try pulling the oil fill cap while at an idle, if it comes off very hard (or not at all) the AOS is toast. We made a test fixture from a brand new oil cap and a vacuum gage that reads 0-20 inches of water; a good AOS should read about 5 inches of water, any higher than that and it needs to be replaced.

Not always as it would depend upon exactly where the leak(s) is(are). Sometimes you simply have to break down and check it with a smoke machine.

Oil fill cap comes off easily and the vacuum is very mild, i can hardly feel it when i put my hand over then oil filler tube but I have been getting more smoke at start up lately. Today it was a pretty thick, whitish blue smoke.

So a failing AOS will create a vacuum leak?

Check your gas cap. A bad gas cap o-ring can cause evap codes and possible a lean condition.

Yes in a way, a working AOS has a low vacuum signal (~5 inches of water) in the engine case, a blown AOS can sometimes be as high as 25 inches of water, which is why it pulls oil into the intake system, which can operate at 25 inches of mercury.

Ok, so I'm making some progress. I pinched off the evap system hose that connects at the throttle body and the MAF values went up to normal, around 13-14 kg/hr, and the fuel trims came down to around 2-3,so it seems the vacuum leak is in the evap system. So which valve should I replace, the shut off valve at the fuel filler or the valve under the left side of the intake manifold? And if it's the valve under the intake manifold, is there a write up on how to do it?

I have had two codes, major leak at the fuel tank ventilation system and PO466, canister shut off valve failure.

I'd start with the canister shut off valve code first.