ES 2.0. 160k miles.
Problem started with code P303 and rough running engine at idle and under acceleration, this is an intermittent issue.
Things I have tried:
1. Replaced coil pack for cylinders 2&3 with a used coil pack (have ordered two new coils and wires, waiting for delivery)
2, Replaced cyl.3 sparkplug (all plugs were replaced 1,000 miles ago)
3.Removed coil electrical connectors and blew out with air, seem to be in good condition.
4. Cleared the engine code

Now the engine is running better and the code has not come back. But there still seems to be an engine miss present. This is a new to us car so do not know if the timing belt has been replaced or not but would think if timing had slipped then the engine would run poorly all of the time.
Questions: 1. Reading appr 1500 ohms between pins 1&2 / infinite ohm between pins 1&3 and pins 3&2. Is this normal??
2, I will be replacing the coil packs and wires once the new parts arrive. Any other suggestions??

 

DTC are starting point to begin looking into the possible cause not the absolute cause of issues and the check engine light . Replacing random parts does not always correct the issue and often distracts from finding the actual cause because DIY fixate on the single cause and not all the possibilities.
When you cleared the DTC all you did was turn off the check engine light.
If the issue was not correct 2 things, you would have found the DTC and maybe other DTC in the permanent file area of the ECU and after 1 to several engine cycles the check engine light WILL be reactivated.
So my suggestion is to either scan directly connecting to the OBDII diagnostic connector with a better-quality scanning device and at least look in the 3 main areas to start looking for the root cause of your problems.
Cant teach diagnostic skills on a single post (it actually takes min several weeks of learning the book work study and then applying in the real world hands on training)...... it just not that easy or there would be more general automotive mechanics actually knowing OBDII diagnostic trouble shooting.


At best at least wait until you have all 4 of your coils and wires boots and springs if applicable ( I did not look up your exact model Mazda) and then start over if the problem persists.
1000 miles and spark plug with your miles is also a possible spark plug issue that should not be overlooked.

 

Installed the new plugs, coil packs and sparkplug wires. Running better but still an issue.
Re-cap:
Original problem Error code P303 and rough idle and very noticeable miss while driving.

Presently:
> No error code present ( I have a cheap-o code reader that doesn't show code history )
> Smooth idle but a miss/stumble after letting out the clutch and initial throttle only when shifting from 1st to 2nd gear ( i could live with it but it's pissing off the wife )
> Runs normal under load and at speed
I've been using the shot gun approach by replacing parts but I just don't have the diagnostic tools or skill level to do any better and these were relatively inexpensive and easy items to replace

My worries are the injectors or the timing belt may have skipped but then I'd expect the problem to be all rpm ranges.
Any more thoughts before I take the car to a pro??
Thanks for your time and consideration

 

By your description again... there should be more information in the ECU. Did you scan the 3 main area's? If not than you are missing vital information.

The other thing to consider before you spend money at a shop is to do a compression test. Easy to do as you have already gained experience removing the spark plugs. Just make sure that when checking each cylinder DO NOT EXCEED 5 revolution of the engine to each cyd or your reading will not be accurate for comparing results.

You could also connect a hand held manual vacuum gauge and see what the needle is reading but that takes a little more information on what to read and how to read it while blipping the throttle and also a slow RPM increase and then fast release of the throttle. But a basic idle reading and seeing if the needle is stead not dancing is helpful.

 

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It's been 3 days and its been running good, think I can say It's fixed!!
rec'd the new plug wires and installed and now the engine idles smoothly and runs with no more hesitation. Something I noticed was the old plug wire for #3 cylinder was missing some of the rubber insulation at the plug end. Possibly it was arcing to ground?
Maybe it was a combination of coils & wires that took care of it, I'm guessing they were original which would have made them 25 yrs old. Anyways, its running normal again and that's all I care about.
Thanks for all the help Callisto, appreciated.

 

Glad to read you got it running well