The CEL code shows P0303, once also P0300, one mechanic changed the coil, then I changed the spark plugs and cables, I also changed the air filter and added fuel injector cleaner to no avail, the problem still persists, the engine shakes, light flashes, would appreciate some guidance.

 

Go to the Adam S post of 04-13-2009 "I have a 2000 Mazda Protege, 1.8L with 5 speed manual transmission @ 190,000 kms"
Run through the inspection and tuneup procedure I outlined there and see if that helps.
(it's cheap and easy to do.)

 

Thanks. However I am still confused as to what to do, the car is well maintained and this does not make sense. Would you recommend a competent Mazda mechanic around Montreal? I read that I should also test the EGR Valve, what do you think? Another thing is that when I changed the spark plugs I noticed that they were somewhat wet inside. Does this mean there is oil or coolant ingress into the cylinder? I really appreciate it.

 

OK;you've got wet plugs, that's got to be gas, coolant. or oil. Which is it? You don't give any history of your car (overheating, last timing belt change, etc. etc. )
If it's gas, that can just be symptomatic of (bad) misfiring, otherwise it's more serious. When you changed the plugs did you use the plugs specified for the engine? If not, you may find this is the problem since Mazdas are very fussy about plug heat range and gap. What color is the porcelain cone around the electrode?
I still strongly advise you to go through the Adam S routine though, because these items are not done as routine per the shop manual and Montreal salt plays hell with the coil pack connectors and insulation and the MAF connector which being up front are exposed to slush. Also the cold winters make the corrugated flex duct between the MAF and the throttle body very brittle in winter, hence susceptible to cracking at the bottom near the throttle body end.
While the EGR valve can be troublesome, it is less common on Canadian cars because years ago, they had a horrible track record in the Canadian climate, so Mazda made a Canadian version of the EGR incorporating a hot water jacket, and now Canadian EGR problems are rarer here than south of the border.
If your wet plugs are due to coolant or oil, then you have a entirely different set of issues to deal with, so find out what that liquid is fast.
As for good mechanics, I have a '99 Protege 5 speed with 95,000 well cared for Km. on it and have had only rare minor problems to deal with. For major service, Mazda 2-20 at 3800 Boul. des Sources (514) 685-5600 has done a fine job for my car.
If you go this route, you should get a hard copy printout of your codes before they clear them another copy after the intervention.