-replaced all 6 ignition coils brand new
-replaced water pump
-replaced fuel pump
-replaced timing belt
-replaced supercharger with a rebuilt one from PSE
-sent the heads out to be machined and valve stem seals replaced
-replaced head gaskets
-had 3 mechanics (none of them from mazda) review the car to try to tell me what is still wrong with it - no answers

after all the work was done it was showing a cylinder 3 misfire code and would hesitate or buck slightly when applying accelerator. Long highway driving was fine. Now it is overheating and showing a cylinder 4 misfire. I'm at a loss with the whole thing. $3000 in parts alone any suggestions?

*Listed the car on RI craigslist if anyone is interested in buying.

 

I'm in the same situation as you. Did you ever diagnose and fix the problem with your Millenia S? My mechanic cannot pinpoint why the car intermittenly misfires when I put into gear when starting it while still warm. Coil. Plugs. Fuel injector. What is it?

 

This is a very old thread and will most likely not be updated by the original poster. Please try to not dig up old threads but start your own, its best that way

 

Ok. How do I start new thread?

 

Old cars are not easy to diagnose as so many things can go wrong. Besides the ones on original posts you can look at: 1) EGR 2) Catalytic Converter 3) Whole ****load of sensors including MAF and 4) throttle body.

On a 13 year old vehicle, sensors don't last and coolant, thermostat should be changed every 2 years.

Here's a list of misfire possibilities:
Vac Leaks
Wiring Issues
Spark Plugs(Even Fresh Spark Plugs That Are Crappy Quality.... E3 And Such)
Ignition Coils
Alternators (Search EMI)
MAFS
Injectors
Injector O-Rings
Intake Gaskets
TB Gaskets
PCV Hoses
PCV’s
Malfunctioning EGR
Malfunctioning CAS
O2 Sensors
Aftermarket Intakes
Intake Hoses
Vac Lines
Timing Chains
Timing Chain Tensioner
Broken Cam Gears
Malfunctioning Cam Sensors
Incorrect Crank Gears(The I4 Has Like 40 Different Configurations For Whatever Reason)
Incorrect PCM Flash
Issues Within The PCM
PCM Wiring
Bad Diaphram Within The FPR
Issues Within The Fuel Pump
Dirty Fuel Filter
Dirty Fuel Lines
Pre-Cats/Poor Exhaust Flow

If the above gaskets/seals have not been changed, change them. Clean your MAF sensor, throttle body.
Change your PCV valve and probably that short hose as well.
Inspect the intake accordian tube for cracks. Inspect for vaccuum leaks.
Put in a good Fuel system cleaner: Red Line Synthetic Oil - Gasoline Fuel Additives - SI-1 Complete Fuel System Cleaner
Inspect wires. Re-set ECU after doing above.

 

This video ( ) mimics exactly the issue with my Millenia-S 1999. But my coils check out.

 

What codes are you getting?

 

Codes:

P0302
P0421 Bank 1
P0431 Bank 2

Replaced coil and plug for cylinder 2. Did not fix.

 

You know, it almost sounds like you have a burned valve on #2, do a compression test on all cylinders.

 

from my experience, mechanical problems with the 2.3 will not throw a code. 0302 is miss on cyl 2. start by moving the coil to another cylinder, and see if the miss goes to that cyl. then the coil is bad. if it stays on 2, try changing or moving the spark plug. moving an injector on this engine is a real pita, but you can ohm them to see, by disconnecting the plug on the end of the rail, and using the spade leads. and sometimes an injector will test good cold, but not hot. same with coils. i just changed a coil that gave a miss when hot. since we have 2 99's, i switched the front bank of coils(since the front is so much easier to get to), and sure enough, the hot miss appeared on the car i switched the coils to. then i started replacing each coil, and after the second one, the miss was gone. no codes were thrown, but i was sure it was a marginal coil. similar symptoms, runs good cold, then slight miss under load when hot. i probably could have found it with a scope, but i dont have one, so i had to go manual. another example of mechanical failure but no codes is a jumped timing belt. this happened last year, the black car jumped time, missed a lot at idle, no codes. even with an electrical problem like a marginal coil, it has to be consistently bad for a specific period of time or cycles before it will throw a code. if you are depending on someone else to diagnose your problem, i think you should move on to someone else who has better diagnostic skills.

0421/31 means bad precat. in your case, both are bad. which may contribute to the miss. when hot and under load, bad precats will cause backpressure. the actual bricks inside are very tightly wound, and highly restrictive. partly because of the problems of forced induction and cats. the post cat sensors are very sensitive. when the car was new, the most common action was to log the date, then erase the codes. if the codes stayed away for a long time, like several months, most likely the precats were still good, and the sensor(s) were overly sensitive. over time, the length of time the codes stayed away would get shorter and shorter, until it became a weekly ordeal to erase the codes, only to have them come right back. this meant the cats were near death, and clogged. changing the front precat is not bad, changing the rear will make you wish you never owned this car. the difference in performance of a 2.3 with new, free flowing exhaust manifolds will be quite profound. the cost will kill you. if you have to pay someone to change them, sell the car now, take the loss, and move on. if you can do the work yourself(and i would NEVER do a rear manifold unless i had a lift), you will be pleased with the increase in performance and fuel economy