Trying to install a new MAF sensor.
The pipe from the MAF sensor to the turbo is pratically welded on to the MAF sensor and does not want to come off.
Any hints on loosening the pipe?

Mine gets that way. Just twist it a bit and pry it off. A little silicon spray might help, especially when trying to put the hose back on.

Use di-electric grease on the coupler when plugging in the MAF.

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Keeping it running is better than buying new

Cannot get the pipe to budge either twisting or bending.
Is heat a no-no?

Plastic to plastic fitting with a metal clamp securing both. Heat is a no-no, unless you mean a warm engine bay. The metal clamp must be really loose. Penetrating oil will not penetrate the fitting as it is all plastic, which is why I suggested silicone spray.

Break it loose first by twisting - then pry it apart.

If your new MAF is just the electrical part that inserts into the housing, can you access the two Phillips screws and remove the old one?
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Keeping it running is better than buying new

Changed the electrical part. Ran great for a day, then started to idle rough again. Now the engine is stalling. Where does one look for vacuum leaks?

Two well hidden vacuum lines: Next to cyl #1 which makes a 180 bend and goes to the PCV valve, and the line going to the air cleaner box, which is then routed under the box.

I suggest removing the cover over the throttle body to expose the vacuum tree. Check all of the lines and caps. Inspect the lines coming from the front of the intake manifold, including the line for the brake.
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Keeping it running is better than buying new

Mine is a turbo.
Does this change the advice?
I gather the throttle body is in a different location than the naturally aspirated engine?

Turbos have different vacuum lines. 4 lines to the turbo, 3 of them routed to the air cleaner box area. You do not have a PCV valve, but a line to the air intake just before the turbo.

If your car failed a glove test, it means that a major vacuum line is plugged or bent closed. If your brakes work normally, then the vacuum for the brakes is just fine.
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Keeping it running is better than buying new

what is a "glove test"?
Can a DIYer do it?

Warmed up engine, not hot, remove the oil cap, wrap a used nitrile glove around the filler hole, start the engine. If the glove inflates, the PCV is blocked. If the glove begins to be sucked into the engine, there is vacuum.
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Keeping it running is better than buying new

The glove partially inflated.
So I guess the PCV plumbing and oil trap need to be serviced.
Is it simplest to replace all the vacuum lines as well when I'm doing the PCV system?

The lines are 13 years old. Most of them will last longer than 20 years, but you need to look at those that get close to heat. Not all are the same inside diameter, and that is important. The elbow connections usually crack first.
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Keeping it running is better than buying new

That was the trick - just popped out the electrical part and replaced it. Easy-peasey. No more codes.
Thanks for the hint.
Is there a good reason to replace the whole body?

Just to make dealers charge more?
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Keeping it running is better than buying new

The sensor attaches to the pipe with a hose clamp, right? Loosen, twist, and wiggle out. I suppose one could apply a some silicone lube to help free things up.

Be sure to look for air leaks and/or cracks in that pipe between the MAF and the turbo.

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XC60 / Odyssey