Rough Idle and Poor Gas Mileage 2.3L

[Throwbot]

Mazda or tomw,
I popped the valve/rocker cover off, and I simply do not know what I am looking at regarding Lifter adjustment. A manual turning of the Cam shows all 8 Valves functioning and moving. The area is Immaculate, like new, very clean. The oil is evenly distributed and all the rollers and cam surfaces are lubricated. I do not know what the position of the piston, opposite the valve, should be. I am concerned that one of those has moved out sufficiently to cause the valve to stay open partially. Or worse, there is a buildup at the valve seat and the lifter/adjuster has compensated, forcing the valve to stay open on cylinder(s) 1 and 4.

Next step is to get a boroscope/camera and look at the piston walls. Perhaps this is all cylinder wall wear.

Regardless, for 165$ I am getting a junk yard motor as soon as possible.

 

[tomw]

The 'lifter' in these is just a support that pushes on one end of the cam follower. The other end pushes on the valve stem. When the cam lobe comes by, it pushes in the middle of the follower. If one end is sitting tight on the valve, and the other end held still, the follower will push down on the valve stem, and open the valve.
If the lifter/support is gummed, it can stand 'too tall' and hold up its end of the follower too high, and the backside of the cam lobe will be enough to hold the follower 'down' and keep the valve open.
With the head off, you can look at the valve 'tulips' and see if the valve seat against the cylinder head when the back of the cam lobe is on the follower. If so, the valve is closed, which is proper. If the lifter is stuck and holds the follower up too high, the valve will not be on the seat. Zero compression follows when in operation.
tom

 

[Throwbot]

Piston Walls are good

I stuck a Camera thru the spark plug holes, and the piston walls all look fantastic. They are clean and shiney and the cross-hatching can still be seen slightly. I was unable to see the valves or their seats, so next is to remove the head, and regardless of status, I will be rebuilding them, with new Valves, New seals, and new Cam-Lifters. I was unable to move the lifters, or adjust them, so I am more convinced that the Valves are stuck open. As this is a non-interference engine, that seems possible.

 

[tomw]

Before you remove the head, do a little more investigating. As clean as the head sounds from your description, it might not have to be removed.
Use a crowbar or long bar of some sort to push the cam follower down on the LIFTER side. After holding pressure for a minute or so, the lifter/support should 'collapse' and get shorter. The oil inside should slowly seep out, and allow the support to compress ~.050 ballpark. If it does, then that lifter is movable. It may have been stuck.
Either way, then try to compress the valve spring. Use your tool on the follower to push down on the top of the valve. The valve should move readily, and when the pressure is removed, should spring back in place.
You can do this with the follower on the 'heel' of the cam lobe, the un-raised part.
You may be able to break free a stuck lifter or valve without disassembly.
If this does not seem to pan out, I would not replace all the valves without inspection. Many many many go a lot of miles without needing replacement. The lifters can be removed from their bore in the head, cleaned, disassembled and checked for worn check valves, etc. Most times, they have deposits that can be removed chemically, and then will work fine. The valves would have to be worn pretty thin before needing replacement. There is a specification in the shop manual for how thick the valve seat area has to be for successful use.
If you had stuck valves in 1 & 4, you'd have zero compression. You might have some carbon or other deposit keeping the valves from seating completely, and thus the low compression. They might be burned exhaust valves, and would need to be replaced. I have a couple sample burned valves with small 'pie' sections burned away. They did not work.
tom