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 Post subject: Miata street car issues
PostPosted: Fri Jul 13, 2018 12:51 pm 
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Joined: Mon Nov 02, 2009 3:47 pm
Posts: 625
Location: The Mountains of Colorado
I have a 96 Miata as a daily driver. 1.8, 5spd 123K. It's developed a bad off idle hesitation. Like, I'm going to die pulling into traffic hesitation. Happens hot or cold. I replaced the fuel pump hoping it was an easy fix.

I do get the occasional P0140 rear oxygen sensor check engine light, even after changing it. How do the SM's defeat this?

Any help or direction appreciated,
Jon

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Mazda Jon
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2009 Mazda MX-5 12A GTL #04
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PostPosted: Fri Jul 13, 2018 4:56 pm 
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Joined: Thu Jun 28, 2012 6:33 am
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Here’s a link to the Spec Miata forum: http://mazdaracers.com/forum/100-spec-miata/


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PostPosted: Sat Jul 14, 2018 7:36 am 
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Joined: Thu Oct 03, 2002 10:34 am
Posts: 2836
Location: Wauwatosa, WI
How is idle?
Does this condition exist using throttle only and not driving, rpm hesitation?
Presume plugs and wires are good.
Coil? Spark under dark/night conditions? Or test coil.
Timing?
Implement a pressure gauge at incoming end of fuel rail/hose to see if new fuel pump is sending desired pressure to rail.
Vacuum leak?
Dirty mass air flow sensor?
Use GRD/TEN jumper in diagnostic box (under hood drivers fender) and the ECU is open loop and the ECU ignores input from the ignition rpm (CAS), temperature (thermosensor at rear of head on the 1.6, 1.8 position???) and throttle position (throttle shaft). If condition exists with jumper wire, rpm, temp and TPS should be eliminated from the picture. Altho I had an issue some years back with my 1.6 where the TPS ohms checked ok and when I installed a new TPS, issue solved. I've since learned another process to check the TPS.

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David Dewhurst
CenDiv Milwaukee Region
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PostPosted: Sat Jul 14, 2018 8:57 am 
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Joined: Fri Dec 23, 2011 6:59 am
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Location: Spring Hill, FL.
Do the David deal.first,
If it runs at WOT OK then the fuel pressure and ignition are usually OK . The tip in is controlled by the TPS and air meter. , with minor correction from the temp senders.

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Mike Ogren/Protech Racing, http://www.FWDracingguide.com http://www.ogren-engineering.com/ 352.428-8983 mogren@tampabay.rr.com


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PostPosted: Sat Jul 14, 2018 10:50 am 
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Joined: Sun Aug 18, 2002 6:16 pm
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Location: Oregon City, Or.
TPS is the most common issue for what you describe, An ohms test will almost never show a problem.. You really need a lab scope to look at the pattern. cheaper to shot gun a TPS

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Joe Harlan Member #175515


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PostPosted: Sat Jul 14, 2018 6:13 pm 
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Joined: Mon Nov 02, 2009 3:47 pm
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Location: The Mountains of Colorado
Thanks guys. This was exactly what I was looking for. I had been looking at the many random Miata forums and basically found it could be anything from a complete engine change to changing the right door handle.

Did the GRN/TEN jumper and it was much better. Took out the jumper and drove to the parts store to get some MAF cleaner and I guess the threat worked as it ran better. Did clean the MAF and it drives sooo much better.

Hope it was this easy, I'll take it for a drive tomorrow.

Thanks for the help,
Jon

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Mazda Jon
AKA Suzuki Jon
2009 Mazda MX-5 12A GTL #04
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