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Engine quits?

Tiny
BRUCE DAVIES
  • MEMBER
  • 1994 MAZDA MIATA
  • 1.8L
  • 4 CYL
  • 2WD
  • MANUAL
  • 120,000 MILES
The car idles smoothly, runs perfectly when accelerating but when I back off of the gas to maintain a speed the engine quits like you turn the key off, but only for 1 to 2 seconds then normal again. This happens repeatedly over and over. Any help would be nice. Thank you.
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Friday, January 12th, 2024 AT 1:33 PM

16 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

That is an odd one. So, the engine stalls but then continues running likely because it is in gear and moving.

Do me a favor. Let's see if there are any diagnostic trouble codes stored. That may point us in the right direction. You don't need a scan tool to retrieve codes. All you need is a short jumper wire or even a paper clip. Follow the directions in this link and let me know the results:

https://www.2carpros.com/articles/diagnostic-trouble-codes-for-1995-and-earlier-mazda-cars-obd1

The data link connector is located under the hood of this vehicle. It should be in front of the driver's side front strut tower. I attached the only pic I was able to find.

Let me know what you find.

Take care,

Joe

See pic below.
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Friday, January 12th, 2024 AT 8:06 PM
Tiny
BRUCE DAVIES
  • MEMBER
  • 9 POSTS
Thank you for your help. A post I read said to unplug the MAS Mass airflow sensor. The computer would go back to its present condition from factory. I did that and all the problems went away. Runs perfect. Will change that tomorrow. Thanks again.
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Saturday, January 13th, 2024 AT 2:01 AM
Tiny
BRUCE DAVIES
  • MEMBER
  • 9 POSTS
I never got a check engine light, and no codes ever came up. Hum.
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Saturday, January 13th, 2024 AT 2:11 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

By disconnecting the sensor, it forces the system into a preset condition. Also, because this is an OBD1 system, there could be codes stored that didn't turn the light on. Have you tried checking for codes?

Let me know.

Joe
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Saturday, January 13th, 2024 AT 3:43 PM
Tiny
BRUCE DAVIES
  • MEMBER
  • 9 POSTS
Yes, and no codes came up. It turned out to be the throttle position senser. I changed that and all is like normal now. Thank you for your help.
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Sunday, January 14th, 2024 AT 4:20 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

Thanks for the update. I'm glad you got it taken care of. Feel free to come back anytime in the future.

Take care,

Joe
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Sunday, January 14th, 2024 AT 7:41 PM
Tiny
BRUCE DAVIES
  • MEMBER
  • 9 POSTS
I'm back again. Now I have replaced the MAS, and the Throttle control sensor. No improvement still randomly skips while driving, but only when I throttle back to maintain a constant speed. Starts good, idles good, and accelerates smoothly. Then just like you turn the key off for about 1 second then runs good again. Any help would be appreciated.
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Sunday, January 21st, 2024 AT 6:15 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

If there are no codes, that is a tough one. Was the fuel pressure within the manufacturer's specifications?

Let me know.

Joe
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Monday, January 22nd, 2024 AT 8:12 PM
Tiny
BRUCE DAVIES
  • MEMBER
  • 9 POSTS
I finely got codes to come up. Code 15, Heated Oxygen sensor inactivation, code 2, 17, Heated Oxygen sensor inversion. Code 3, 14, Barometric absolute pressure sensor. Code 4, Throttle position sensor. I changed the Throttle PS re-set the codes to 0 and then drove the car 15 miles. Still same problem but no, no codes again.
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Tuesday, January 23rd, 2024 AT 9:34 AM
Tiny
BRUCE DAVIES
  • MEMBER
  • 9 POSTS
This thing is driving me crazy, hahaha. I have been working on cars since I was 15 and never have so many problems fixing a engine. Any help would be very appreciated. Now it's either me or the car. Whose going to win?
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Tuesday, January 23rd, 2024 AT 9:38 AM
Tiny
BRUCE DAVIES
  • MEMBER
  • 9 POSTS
What's your thoughts on a Crankshaft position sensor?
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Tuesday, January 23rd, 2024 AT 2:07 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

A crankshaft position sensor will cause ignition problems if it is failing. Do me a favor. Take a look through this link and let me know if you feel anything mirrors what you are experiencing:

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

Also, yes, the sensor or a connection at the crankshaft sensor can cause this. However, the one code that has my attention is related to the MAP sensor, code 14. On this vehicle, the barometric pressure sensor is integral to the PCME. When code 14 is set, the PCME itself is usually the problem and needs to be replaced. See pic below.

The PCME (powertrain control module) is located behind the passenger seat. I have a feeling this is where the problem is coming from. Interestingly, it can't be tested independently. That is where the manual says to replace the PCEM if code 14 is set.

Let me know your thoughts.

Take care,

joe
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Tuesday, January 23rd, 2024 AT 7:47 PM
Tiny
BRUCE DAVIES
  • MEMBER
  • 9 POSTS
Hi Joe. Well, I changed the Computer, And the MAS, TPS, but still have the same problem. Only after the engine warms up. Driving down the freeway at 70+ it runs perfectly but under 70 it's just like you turn the key off and on. Not constant but all the time. Just don't know what else to look for. Any suggestions? OH, and still no codes.
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Tuesday, January 30th, 2024 AT 5:40 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

Did you ever replace the crankshaft position sensor? Also, you disconnected the MAP sensor, and it ran normally. I realize you replaced it, but there could be a connector or wiring issue. Did everything appear to be in good condition?

Joe
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Tuesday, January 30th, 2024 AT 8:08 PM
Tiny
BRUCE DAVIES
  • MEMBER
  • 9 POSTS
Hi. The only thing that has made a difference was unplugging the fuel positioning sensor. That made the engine run smooth and idle normally, but still cut out while driving. Unplugging the MAS didn't do anything. I just changed the main computer with NO change, still cuts out. Yesterday I ordered a Crankshaft position senser but after ordering it I saw a post that said that 1994 doesn't have one. The Cam position sensor and the Crankshaft sensor are one and the same, All one unit. Is this correct? One site says yes, another site says no. The Cam sensor is expensive [around $ 200 +] so would like to hear your thoughts on this before ordering a new one. Thank you so much for your help with this problem. You're providing a really wonderful service to people who really need help.
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Thursday, February 1st, 2024 AT 8:13 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

The only thing my manual shows is a crankshaft position sensor. I attached a pic below. Note that it is located at the rear of the cylinder head near the coil.

Additionally, if I am reading the directions correctly, it is used to adjust ignition timing.

Take a look and let me know if you find this in your vehicle. And it does look like an expensive part on this engine.

Let me know.

Joe

See pic below.
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Thursday, February 1st, 2024 AT 6:16 PM

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