My son's 02 Protege quit running on him as he was driving. He said the engine seemed to just start shaking and then the car just quit. It turns but does not start. We're getting codes of P0401 and P0340.

I removed valve cover and inspected the timing belt. The belt appears to be in good shape.

Any suggestions?

 

Could be anything at this point.
look up the codes online.
what's the mileage on the Protege?
Was there recent work done?

 

p0401could be any of the above, though ill tell you the most COMMONLY replaced part is the boost sensor


p0340
most likely this code relates to the Mass Air Flow sensor (MAF)

EGR valves new or reman run between 170-190 bucs
MAF sensors run between 195-270 bucks
Boos sensor runs about 135.

all expensive parts but thats what you should expect with a protege

 

Try replacing the boost sensor 1st.
You can find the part online.
You can also find it used.
Remove the sensor 1st and look at the unique part#.
I've seen the parts on ebay also. A lot of the sellers offer returns.

Try the above.

I had approx. 135K on my Protege 5 and next thing you know the Air hose literally fell apart. If there's any kind of crack in the air-hose it will make your engine run like crap, almost likes it's going to turn off.
If you do find the air-hose cracked or needs replacing go to:

Onlinemazdaparts.com

They have it there for $47 plus S&H.

If all else fails, take it to a reputable mechanic. They have the equipment and experience to diagnose the problem.

 

I think vivamiguel is on the right track, but I would not immediately jump to replacing sensors and valves. I like to inspect, clean and reuse.

Also make sure that the vacuum lines are ok. Here I like to replace immediately because it is cheap and eliminates a lot of potential future problems. You can buy vacuum line by the foot from the reel.
Pay particular attention to the vacuum line that goes from the intake manifold to the EGR boost sensor which is mounted on the fire wall. At the intake manifold that line is attached to a nipple. Use a strong wire or small allen wrench and push into that nipple. If you have resistance it is clogged. It must be open.

good luck