warm 2.3 engine misfires at speed - Mazda Forum
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post #1 of 6 (permalink) Old 03-27-2017, 07:18 PM Thread Starter
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warm 2.3 engine misfires at speed

Hi all- I have a 2.3 Milli S 1998 w/ 195,000 miles. It starts, idles and runs great when below normal operating temp. I have a 505 code and the Mazda service mgr. suggested just disconnecting the wire to the IAC therefore engine light is on constantly. He said no big deal. It idles about 1800 rpm when warmed up. The BIG ISSUE - I get an intermittent misfire on the freeway at around 65mph that comes and goes. If I slow down to 50 it goes away and may - or may not - come back. Going uphill or downhill doesn't seem to matter. It sounds like a popcorn popper machine as the misfires are not cyclical. All 6 coils and spark plugs were just replaced with $$ new ones. Issue remains as before. Any thoughts from the genius' here? Local mechanics + dealer are stumped. Thanks.
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post #2 of 6 (permalink) Old 04-11-2017, 03:38 AM Thread Starter
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Since this only happens when the car is at full temp. would changing to a cooler thermostat solve the issue?
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post #3 of 6 (permalink) Old 04-11-2017, 08:12 AM
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Hi Karl,

I think this video should be looked at. It shows an excellent case study on another car which is a Lexus ES300.
(It's not based on a Millenia "S" but should help out when left stumped with strange misfire issues...)

Please post back your fix if you find out what was wrong with your 2.3's ('S' model) situation.

Best Of Luck!

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post #4 of 6 (permalink) Old 04-16-2017, 01:25 AM
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What cylinder is the misfire? When's last time the timing belt and all idler pulleys were changed? I had similar issue engine would suddenly cut out only at freeway speeds, turns out one of my idler pulleys broke apart it's plastic lining and the timing was jumping causing the engine to cut off.

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98 Millenia S 2.3, cabin filter mod, Valve Covers not Leaking, working tilt, New timing set, waterpump, 17" Rims, K&N drop-in filter, HIR2 9012 Headlights, 12" Diamond D6 Subwoofer, GroundShaker Ported Enclosure, Kenwood 1200watt Amp, Blutooth
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post #5 of 6 (permalink) Old 04-16-2017, 05:10 AM
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miller cycle i expect??
I worked on one years ago with a leak on the inlet gasket to s, charger, from memory it made noises like that and miss-fired..
Just a thought.. Was a long time ago, think was metal gasket.. Been on gas analyses?? Lean might point in that direction..
Good luck
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post #6 of 6 (permalink) Old 05-13-2017, 09:32 AM
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It is this the costly dilemma I hope to avoid by my recent post 'P0303 (misfire cylinder 3) at 38K miles on 2.3L engine'. I'm no 2.3L engine expert but know this engine can defy the experts sometimes. Perhaps the weirdest cases get the most attention and the frequency of such cases is therefore exaggerated, but I suppose that leads to some paranoia on my part and failure to recognize when a problem is likely to be routine. My Millenia is still parked as I decide what to do.

If you are unaware, you can find DTC info at milleniatech.net, but what's there about P0505 is only the summary "Idle-air control (IAC) circuit malfunction" which is not so helpful. A TSB about misfires #0102702 , recommended to "use a suitable top-engine cleaner" to "decarb" the engine and to use 87 or 89 octane fuel in the future. From an expert I trust, I received contrary information about the first part of that recommendation due to such treatments being harsh on rubber components that can lead to engine problems, and no feedback yet on the second portion (lower octane fuel). Do you not get the "combustion misfire detected" codes (P0301-P0306) after one or two of these misfire episodes? If not, I wonder if there is a clue in that.

I appreciate seeing some ideas in replies about potentially-related issues in this post. The one about the timing belt made me try to remember talking with rebuilder of my engine about timing belt adjustments. On another engine he rebuilt (of my Mazda B2600) I was supposed to bring it back for tightening after 20K miles, but on the Milennia 2.3L, I think there was an auto-adjustment mechanism that was supposed to make it unnecessary. My memory is not as good as it used to be, so that should be verified. Good luck! And please post what ends up being wrong (assuming you find out).

Last edited by OldMazzies; 05-13-2017 at 09:38 AM.
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