Son has a mazda protege dx runs rough when cold, backfires through intake, gasoline in oil, thinking idle air, but could it be injectors?

This problem is a bit more difficult to diagnose because half of your symptoms rule out half of the solutions. I would think the ISC control could be dirty or not working or your fuel injectors are sticking open.

With black exhaust smoke you are running rich. Often the "Cold start sequence" is at fault for poor starts making the engine too lean when the sequence fails. An intake air leak can cause the engine to run Rich, causing the black smoke, rough idle, rough running conditions. This is still a possibility, but the on-board computer usually sets a Code saying you are running "Lean" and then enriches the fuel ratio and floods the engine by itself.

Now the fuel injectors can cause several of your problems. For start-up problems, the remaining fuel pressure can dump fuel into the engine as the car sits because the injectors are sticking open. Someone would need to perform a fuel pressure bleed-down test to see if you have this problem.

Another way to verify this problem is to capture the oil during an oil change and smell it for gasoline fumes. The dilution of the oil will destroy the engine. If the injectors are found to be the problem, a new oil filter and change are needed.

ck fuel pressure ,map maf sensor.timing .

Sometthing to think about. When it is cold the engine it runs in close loop, after it warms up it gos to open loop.

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Could be the Mass Air Flow sensor. But I would check the cold air intake tube first, they are subject to cracking and any hole in it will cause the MAF to give false readings which will trigger the light and cause rough idle, stalling and hesitation.

Check the air inlet boot going from the air filter to the intake for rips or holes. If rips exist, this would allow air to bypass the filter and mass air flow sensor and will lead to a check engine light appearing. The code would read "too lean, bank 1." If this problem is allowed to continue for long periods of time, the EGR ports will have to be cleaned out and maybe even the intake.

o2 sensor

What is a gasoline valve? If you are looking for your fuel injectors, they are on the fuel rail that runs along the the intake manifold. If you're looking to put gas in, there is a latch on the floor between the driver's seat and the door which opens the gas door. Do you have your owner's manual?

you need to FILTER the air coming in the intake with something screen or something zip ty some screen and paper towel .then give it an oil change and clean the plugs(do this first).

The idle on my 2003 Mazda Protege started acting strange one day - it kinda surged forward a little bit. Then the RPM would drop and kept wanting to stall out. It stalled out at a stop sign. The check engine light came on. I drove it immediately to my Goodyear mechanic. It ended up being the Idle Air Control Valve. They had to order the part from Mazda which took 3 days to get there. The whole thing cost $700. Runs great now (again).

change the transmission fluid, replace the oil and oil filter check spark plug cables, check starter coilpak, and make sure there is coolant