Need help please. Car shop says I need to replace intake Manifold
 

https://cimg9.ibsrv.net/gimg/www.rx8...37f5d26291.jpg
This is what I got. I’m out of town and went to a random mechanic. Had Rebuilt engine put in about a year ago.

P0076 generally doesn't require (pretty much never) an entire intake manifold replacement. It's likely the solenoid but there's a whole lot of diagnostics that can be done on that. The misfire may be related to the too lean/vacuum leak issue, sort that out while checking into the VDI valve issue (P0076) and check spark plugs then coils.

You have bigger problems than that, the p0420. The conclusion is right you may have low compression and need a new engine. You may also need new coils. They should be replaced every 25k miles or so. You can worry about troubleshooting the intake after that.

Next stop should be a Mazda dealer or local rotary specialist.

Also you may want to remove your name, address, phone number, email, vin number and license plate from stuff you post on the internet.

Probably just a leak in the intake but your cat is likely damaged. This is the first and most important thing to check.

Compression check, coils, plug condition, cat ion that order. Stop when one of the things you're checking fails. If compression is ok, check the coils...if they're original, they're likely toast. Check plugs, then see if the cat is clogged/damaged

This mechanic practically wants to stop working for the rest of the year after fixing all these diagnoses. I think you just need to grab some esencial tools Jack Up the car Take the mid pipe off and make sure (the cat can be clogged as mentioned) (mine was) then go check all the hoses from the intake Only one of them in the wrong place can cause misfire especially when idling, check connectors, the grounds. It could be a lot of things but if you have a least some time you can check all this. The O2 sensor I think is not a big deal... Screeching noise when turning “come on” probably the brake rotor has some dust on It. If It runs It must have compression (you can figure that out with a regular tester)
https://youtu.be/iXZU7KKW6nc

also premixing will help a lot for better sealing and of course to keep your engine alive :)