Odd Idle Issue 1987 b2000

I really do appreciate the advice though,I am determined to get this solved!

"I will do another compression test tomorrow though, initially I did one before I sent the head off and they were all consistently low ( all in the 110 range). I was hoping that having the head machined would fix the issue but it didn't :/ "

For the compression test, all four plugs should be out, and the throttle wired up (or pedal held down fully) during the cranking. Cranking speed should be pretty good, and held cranking at minimum several revolutions.

For reference, at 183K miles on my 1988, the compression measured 165 psi on all four cylinders. So I am skeptical about the reading of 110 psi in all four cylinders on yours; but if that reading is confirmed, that would be a huge clue.

I'm toying with taking compression numbers on mine this weekend, at 212K miles now.

If you have a vacuum gauge, you can connect it to manifold vacuum and while the engine is running, disconnect one plug at a time and record each value, it will show you which cylinder does not drop as much vacuum as the others. That is the first test that should have been done before anything else was done to eliminate problems with the pumping action of the pistons on each cylinder. A bad cylinder won't drop as much vacuum when it is taken out of the mix. You have spent a lot of money and time chasing this problem and I think a 110 psi should have provided another clue that the bottom end of the engine i.e. the rings were worn out. Looking at the cross hatching on the cylinder walls when the head was off won't tell you anything about the rings. How many miles do you have on the engine? The compression minimum for a slap worn out engine is 120 psi, so what you indicate about getting 110 across all four cylinders indicates that maybe something wasn't quite right with the test. As Cuser said, the throttle needs to be wide open while the test is being done, with plugs out of the head. The engine needs to be cranked around about 5 times for the cylinder being tested and the findings written down. While the engine is being cranked, the gauge needs to be looked at to see if the needle jumps up stoutly or just limps up to a maximum value. After a dry test is done, a wet test needs to be done on the same cylinder and the results recorded to indicate wear conditions of the rings. A wet test is done where the gauge is removed and about two tablespoons of oil are poured into the cylinder and then retested.

Ha it was a pretty crappy worn out tester rented from autozone,

Soo for an update, we went out and bought a nice new compression tester! the new readings are as follows
cylinder 1 -177, cylinder 2 -181, cylinder 3 - 171, cylinder 4 - 179

i will do another test after work to double check, and i promise ive taken all of the plugs out, cranked it around 4-6 times each with the pedal to the ground.

the engine has 173,xxx miles on it. I do like the vacuum gauge idea though and will try that next, thank you all again and i will keep you posted

This issue has even stumped our mechanics friends, 99% of the work has been done in house by my father and I, But we took this two different mechanics and not even they solved it :( so at this point im starting to think it is some odd rare issue

Sooo I have an odd/ possibly stupid idea and would like y'alls opinion on it. Could this issue possibly be caused by a faulty radio condenser wire? this is the wire located on the distributor and it cancels out interference noise but it also stabilizes current around the distributor. When the issue started and when I changed the distributor to try and fix the issue, the wire was old and rotted, and at the advice of a mechanic friend I pulled it off because he said it was not necessary, but the more I think about this issue the more i think it could be electrical (Especially since the issue came up out of nowhere with no warning) and there is not much electrical stuff left to change. thoughts?

That's not a dumb idea. I had that part go bad on mine, the wire got hard and broke. At first I dug into the plastic and soldered on a new wire. But what I have now on there is an inexpensive condenser that would be used on an old Volkswagen Beetle (like a 1970 model) there instead. https://www.google.com/#q=volkswagen+distributor+condenser&* I really don't know enough about that to know if its job is 100% static reduction, or if it also helps with the spark; I know on the old VWs that it is absolutely necessary.

These could be purchased through NAPA, O'Reilly, Autozone, and some stores may stock them, or try a parts store for imports if there's one near you. The official Mazda part may also be available (online or order from dealer), but I don't have a part number or even the "correct" name to help search out a source; you may have to call or stop by a Mazda dealer for that.

Another thing that wouldn't hurt would be to run the engine when it's dark or mostly dark, and look for spark jumping; even mist the distributor and spark plugs with water from a spray bottle can make this even more visible. Dirty engine, spark wire supports, lots of things can be routes for spark jumping.

It occurred to me to suggest that you can try this to check for block leakage. With the engine cold, remove the radiator cap. With the cap off, start the engine and let it warm up to operating temperature. Once that occurs, look down the radiator neck and watch for bubbles. That indicates that compression gas is being pushed into the water jacket. There is a chance that the block has some warpage to it and even though the psi on the cylinders look pretty good, warpage in the block is preventing a good seal between the head and block. You can try to retorque the head if the bubbling isn't too severe.

Sorry it took so long to respond, i have been crazy busy lately, but it is fixed!!!!

The egr valve was stuck open so when we put the block off plate on it ran like a champ, and I am so happy to have her back :)

Thank you guys for all the advice, after changing everything the truck is running better than it has in the past 10 years!

Glad to hear it is running better. Odd symptoms you were having to come down to an EGR valve. Seems that would have degraded the idle all the way across all four cylinders, but glad it's fixed for you.