Heres one for the more technically minded...

My rex since the weekend has developed a bad misfire, first I thought it was dodgy fuel, but after a fresh tank it has continued.

The problem i was experiencing was revs fluctuating about 100 rmp every 2 secs, very noticable if you watch the boost gauge also, and misfiring at 1/2 throttle to full throttle conditions.

So I cleaned the airflow meter with contact cleaner and the idle stepper motor and sprayed a whole heap of upper engine cleaner in the manifold and through the IAC valve hole to clean it all. Then left the battery disconnected all night to reset the computer.

The problem seems to have gotten worse now...

Now the fluctuating idle has gone, but an annoying misfire is now present all the time at 1/2 throttle conditions, but seems to be ok at slight throttle and full throttle conditions. The misfire is causing the car to jerk and stutter like a POS!!

Any ideas? I read the CEL codes last night, and 23 or 24(can't remember) and 33 were flashing up. The CEL light has not displayed while any of the misfires have been occuring.

I just don't want to replace anything that doesn't need replacing...

take it to a workshop.

fouled plugs, bad fuel, fuel filter or so much detonation that the spark electrodes are rooted.

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Long live the WRC

money on the spark plugs
I had smilar issue - one of the plug electrodes was found to be 'melted/missing'

do you have a POD or CAI ?

I bet your AFM is fouled from an oiled air filter...

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Mazda CX-7
Mitsubishi Evo X MR

sounds like your AFM is stuffed from using oiled filters. Causing your engine to lean out and one of your plugs got melted. Or engine is leaning out now and your getting pre-ignition detonation from an over lean mixture.

Take your spark plugs out and check them.

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RS Liberty - Because WRX's are only good for parts...

In my experience giving problems like this to a workshop to diagnose, ends up resulting in lots of money being spent, and often parts being replaced that don't need to be.... so, I hope to diagnose this problem based on what info I find out here. I believe People should learn how to fix problems on their own, without always having to run to a workshop all the time. Workshop is a last resort. Sorry to rant, but if I wanted to get a workshop to diagnose the problem, I wouldn't be asking for the advice of people on this site....

Cheers Tuna, will check the plugs and report back...

Afm...

Well, checked plugs no sign of a cylinder not firing and totally intact. Checked all the leads for resistance all spot on. Cleaned all electrical connectors, re cleaned AFM element, cleaned IAC stepper motor and sprayed some upper engine cleaner in for good measure.

Still, got the problem?! To top it all off, the CEL light is NOT indicating any faults? Could any faults be showing up under an OBDII check that the CEL codes cannot display?

Anyone got a Tactrix or similar OBD2 cable they feel like lending out for a day or so?

got the cable and the software, PM me for my contact info

i had a similar problem and although the resistance on the cables read perfect i noticed one of the cables (the connector on it) being a lot darker than the other ones...i replaced all four cables (never replace just one...not worth the effor) and it went away....just magic

PM for the cable, i've got a laptop with the software too, and i understand your approach coz a workshop will change the AMF, plugs, cables etc and you end up paying $1000 or so, not worth it.

Also CEL 23 - Mass Air Flow Sensor Circuit
CEL 24 - Idle Control System Malfunction
CEL 24 - ISC VALVE (Stick)
CEL 33 - Vehicle Speed Sensor