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Discussion Starter · #1 ·
Hey guys, I need some help
This just started, when I give the car gas it will randomly misfire and sometimes it won't. But this is a really stressful prob. I'm no sure where to start. I also know the codes I'm pulling if that helps. Its a 1999 drive train and ecu

Things I've tried:
New plugs
new fuel filter
cleaned the CPS (camshaft position sensor)


P1505
idle air control
solenoid circuit
intermittent falt
(no clue where to start)

P1135
HO2S11
heater circuit low input
(i think my fuel/air gauge spread the signal too thin)

P0420
catalyst system
efficiency low
(no cat, lol)

P0300
Random/multiple cylinder misfire



Someone told me to clean/replace the IAC I'll look at it today.
 

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check your coilpacks and precat o2 sensor. i had the same problems, changed them and now im good. pull the wires from the coilpacks and inspect where the wires plug into. mine looked chewed into, and plastic got into the base. it's a big problem for 99-00 miatas.
 

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Clean the throttle body and top of the intake mani. Clean the stupid ass EGR stuff too in the up intake manifold and the EGR valve.

The random misfire is typically a coilpack problem from what the majority claims, the other problems can easily stem from the misfire. 99 ignitions are ****!
 

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Discussion Starter · #4 ·
Thanks guys for your help after a ton of trouble shotting and replacing of parts we found that I needed new plugs and the filter before the fuel pump was clogged with a clear goo for now everything is good
 

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Usually the coilpack is the miata's one weak link. I've replaced my 01's twice in 110K miles
 
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