2005 GMC Envoy XL 4x4 4.2l PO172 enigne too rich

Could be catalytic converters clogged. Remove the pre O2 sensors, or loosen the exhaust at the manifold. If it goes faster, replace the cats. Have the codes read.

No recall on manifold cracking.

P0172 CHEVROLET - Fuel Trim System Rich Bank 1

Possible causes- Faulty front heated oxygen sensor

- Ignition misfiring
- Faulty fuel injectors

- Exhaust gas leaks

- Incorrect fuel pressure

- Faulty Mass Air Flow (MAF) sensor

have you checked for a vacuum leak?pcv attached,no leaks around plenum,engine coolant temp sensor reading right.

Here is a brief description of the codes;
P0141 - rear O2 sensor
P0172 - system too rich
P0606 - PCM internal failure
P0014 - Camshaft phasing off
P0016 - Camshaft position and crankshaft position off

This going to require a qualified technician to diagnose. The PCM issue may require a reflash of its memory or a replacement.
The other codes could be related to each other. One suspect item is the camshaft position actuator, sometimes it gets clogged with oil and make it fail.

Quick and easy way is while the vehicle is running get a can of carburator spray and start to spray in areas where there are vacuum lines or places for vacuum leaks like the intake manifold. If the idle changes in a area when you are sprying it, you will know the vacuum leak is in that area and you can narrow it down from there. I have special tools for this but use them on a regular basis so i need them and they do cost. I hope this helps you and good luck.

Depends on where the leak is. There is a known problem with exhaust manifolds cracking on these trucks. If that is the case, the manifold needs to be replaced. It is also possible that the manifold bolts have come loose.

Check the intake manifold for loose or leaking hoses. Also, clean your throttle body with throttle body cleaner, WITH the battery disconnected. After done, drive for 5 miles or so.

You have a leak in the air system. You can replace it with regular suspension parts.