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Old 24-04-2015, 04:23 PM   #1
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Join Date: Apr 2015
Location: Australia
Car: 2003 Mazda 323 SP20
Posts: 3
2003 323 Sp20 rough idle and carbon spitting exhaust

My 2003 Mazda 323 SP20 is having some issues at the moment. It idles rough once the engine has warmed up. It starts up and runs smooth then after 10 minutes of idling it gradually gets worse shaking a bit. Every now and then it does a big drop in rpm for a second then goes back up. The exhasut smells very fumey and is spitting out black carbon stuff. This has started after i have been to the mechanics. I changed the air intake from an aftermarket one to the stock one about a week ago. then went to the mechanics to fix a misfire in the engine. They changed spark plugs and leads and ignition coils. This fixed the misfire but now it has a rough idle. The black carbon would sometimes happen after being driven a bit harder than usual but now does it just from idling. Is it running too rich and need some tune up or something.
Any help would be appreciated.
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Old 27-04-2015, 06:52 PM   #2
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Join Date: Jul 2011
Location: Melbourne Vic
Car: 2003 Protege Sp20
Posts: 642
One thing it that comes too mind is a dirty EGR valve. I haven't cleaned the one on my car yet but it displays some of the same symptoms you describe. Good place to start or google Protege EGR and have a read.

Sure there will be other suggestions from the much more mechanically minded around here.
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Old 27-04-2015, 09:31 PM   #3
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Join Date: Oct 2005
Location: Ipswich, Queensland
Car: 2002 Mazda Astina SP20 2006 Mazda 6 GY Wagon
Posts: 9,769
Could be a number of things:

EGR Sensor
o2 Sensor
coils (even new ones can be bad straight from the box)

Also you said you changed from the an aftermarket intake back to the stock unit, check the rubber pipe that goes between the Throttle Body & MAF, they tend to crack at the flex bend.
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Old 28-04-2015, 09:56 AM   #4
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Join Date: Nov 2006
Location: Brisbane
Car: Mazda SP20 sedan
Posts: 1,769
Reset the ecu.

Disconnect the battery, press the brake pedal to use up residual charge. Then reconnect the battery and take it for a drive.

Exhaust: Autoexe headers; Custom midpipe; Racing Beat catback
Engine: AWR mounts; Twiggy cams; Custom CAI; RR Racing UDP; Mishimoto rad
EMS: Microtech LT-10; J&S Safeguard;
Gearbox: MSP LSD; Fidanza flywheel; 5th gear
Rims/Suspension: MX-5 rims; Tokico Illuminas; Eibach Pro-kit; Progress RSB; AutoExe STB
Exterior: MSP front lip & rear spoiler; Matt V headlights; AutoExe grill; EDM tails
Interior: JVC AVX-77; Autometer gauges; DaveBs; B&M shifter
Projects to come: Engine rebuild
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Old 28-04-2015, 06:00 PM   #5
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Join Date: Apr 2015
Location: Australia
Car: 2003 Mazda 323 SP20
Posts: 3
Thanks for the reply guys turned out to be a leaking vacuum hose after the MAF sensor. This sucked in more air making it run lean. It then overcompensated and made it run rich.
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carbon, exhaust, idle, rough, smell

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