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Old 11-21-2007, 04:40 PM   #1
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Default Weird ignition gremlin -- acts like bad plugs and wires, but isn't

I've felt a car with old plugs in it before, and the behavior of my car is pretty similar. It runs rough when cold, almost like one cylinder isn't firing. It smooths out when it's warm, though blipping the throttle for a downshift still feels sluggish and stuttery, like I really have to put my foot into it to make it cooperate.

I've replaced the plugs and wires and checked for trouble codes. Everything seems groovy, though one weird thing: twice, when taking the car out for a test drive after working on it, it seemed to be fixed. But the next time I started it, it went back to stuttering. Those two times were the plugs+wires, and fuel filter+tranny fluid. Maybe it's just the placebo effect, fucked if I know.

Actually one more weird behavior my car has is that it's EXTREMELY quick to start, like fuel gets ignited and the motor begins going during the first turn of the crank. That used to alternate with hard starts (cold) but something I've done in the past month or two has fixed that, now it's just quick starts.

Should I try new coils? Could a clogged cat cause this (I had to cheat to pass smog last time)? I never thought of this, but my timing is advanced and I haven't tried putting it back to 10. Could that cause it?
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Old 11-21-2007, 04:52 PM   #2
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check you engine ground, you car is gettin old, it can go bad
a cat could contribute to sluggish beahvior
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Old 11-21-2007, 05:27 PM   #3
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hows your o2 sensor?
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Old 11-21-2007, 05:42 PM   #4
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Sounds like it could be a bad ground... Check them all. On my '97 there are 4 that I know of. I have to clean them all about once every 2 years or the car starts running like poo.
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Old 11-21-2007, 06:11 PM   #5
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Quote:
Originally Posted by Latch View Post
I've felt a car with old plugs in it before, and the behavior of my car is pretty similar. It runs rough when cold, almost like one cylinder isn't firing. It smooths out when it's warm, though blipping the throttle for a downshift still feels sluggish and stuttery, like I really have to put my foot into it to make it cooperate.

I've replaced the plugs and wires and checked for trouble codes. Everything seems groovy, though one weird thing: twice, when taking the car out for a test drive after working on it, it seemed to be fixed. But the next time I started it, it went back to stuttering. Those two times were the plugs+wires, and fuel filter+tranny fluid. Maybe it's just the placebo effect, fucked if I know.

Actually one more weird behavior my car has is that it's EXTREMELY quick to start, like fuel gets ignited and the motor begins going during the first turn of the crank. That used to alternate with hard starts (cold) but something I've done in the past month or two has fixed that, now it's just quick starts.

Should I try new coils? Could a clogged cat cause this (I had to cheat to pass smog last time)? I never thought of this, but my timing is advanced and I haven't tried putting it back to 10. Could that cause it?
Clean the AFM contact pads and tighten the brush against them.
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Old 11-21-2007, 07:12 PM   #6
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Quote:
Originally Posted by Braineack View Post
hows your o2 sensor?
The PO claimed he replaced it very recently, but who knows. Shouldn't the car still be in open-loop when it's started cold?

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Originally Posted by Arkmage View Post
Sounds like it could be a bad ground... Check them all. On my '97 there are 4 that I know of. I have to clean them all about once every 2 years or the car starts running like poo.
I've never checked that. I see then randomly around the underbody... I guess I just undo the bolt and rough up the contacts with a wire brush?

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Clean the AFM contact pads and tighten the brush against them.
I never thought about that, but it would make sense regarding the hesitant throttle blip. Does the ECU use data from the AFM to start and idle? (Sorry, I'm an engine management noob.)
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Old 06-15-2009, 09:16 PM   #7
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Well, fast forward a year and a half, and I've replaced everything I thought it could be. New fuel pump and filter, COPs, eliminated the AFM with a Megasquirt, cleaned injectors, replaced all hoses and made sure there were no vacuum leaks, tested the TPS... And I still have this weird stutter when opening the throttle. The car has done this since I first bought it, pre-turbo.

Here's a video of it happening.

YouTube - Miata Stutter

Any ideas?
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Old 06-15-2009, 09:43 PM   #8
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Quote:
Originally Posted by Latch View Post
It runs rough when cold, almost like one cylinder isn't firing. It smooths out when it's warm, though blipping the throttle for a downshift still feels sluggish and stuttery, like I really have to put my foot into it to make it cooperate.

I've replaced the plugs and wires and checked for trouble codes. Everything seems groovy, though one weird thing: twice, when taking the car out for a test drive after working on it, it seemed to be fixed. But the next time I started it, it went back to stuttering. Those two times were the plugs+wires, and fuel filter+tranny fluid. Maybe it's just the placebo effect, fucked if I know.

Actually one more weird behavior my car has is that it's EXTREMELY quick to start, like fuel gets ignited and the motor begins going during the first turn of the crank. That used to alternate with hard starts (cold) but something I've done in the past month or two has fixed that, now it's just quick starts.
Isn't this quite obviously a problem with MS startup settings?

Take the time to search recent posts about CPW, fixed MAP, ASE, and Warmup Wizard. I did, and now my car starts perfectly in all temperatures.
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Old 06-15-2009, 09:54 PM   #9
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Nope, it did the same thing bone stock. To clarify, the cold start isn't a problem anymore, but I thought it was related to the hesitation when opening the throttle, when I started this thread 10000 years ago.

Last edited by Latch; 06-15-2009 at 09:59 PM. Reason: to crarify
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Old 06-15-2009, 10:40 PM   #10
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Sorry, I didn't notice the dates.

The more I learn about tuning my MS, the more I realize that many "problems" people cite here just boil down to improper settings.
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