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If there still is a leak in the intake manifold, it will be impossible for the MAF sensor to get an accurate reading. Without knowing how much air is really getting into the engine. To accurately check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg (inches of Mercury). At 3,000 RPM, it should be around 21 InHg. If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.
If you are getting P0101 accompanied by a noticeable lack in power at speed, it may very well be that you have a clogged catalytic converter. Here's how to test it:
With a vacuum gauge attached to a full vacuum source, at idle, the vacuum reading should be between 18 - 20 in-Hg.
Now increase and hold speed to about 3000 RPM. The vacuum reading should drop but should go back to the previous level in a few seconds; otherwise, it's likely the exhaust system is blocked. Continue to the next step.
Repeat the test, but this time, snap the throttle valve open about four times, rising the engine speed to about 2500 RPM. Take note of the vacuum reading with each snap of the throttle. If you see that gauge needle dropping steadily to near zero, most likely the catalytic converter or muffler is restricted.
