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| Erratic Idle, Backfiring (Page 6/6) |
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fierosound
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SEP 17, 10:27 PM
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| quote | Originally posted by Addition1291:
Aaand we're back. Kind of.
So the car runs fine now. Idles well and drives ok. There's just one last problem I'm having that might be related. |
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Any ECM codes?
http://www.fiero.nl/cgi-bin/main.cgi?ECMCodes
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Addition1291
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SEP 18, 12:02 PM
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Yeah. Looks like a code 23 and 33. 23 Doesn't make a lot of sense to me. I just replaced the MAT sensor but maybe I bumped it loose when I was messing around with my slave cylinder earlier. I'll have to check that connection.
33 Is interesting. I don't think I have any vacuum leaks but I could be wrong. I'll have to check again
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fierosound
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SEP 18, 12:14 PM
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| quote | Originally posted by Addition1291:
Yeah. Looks like a code 23 and 33. 23 Doesn't make a lot of sense to me. I just replaced the MAT sensor but maybe I bumped it loose when I was messing around with my slave cylinder earlier. I'll have to check that connection.
33 Is interesting. I don't think I have any vacuum leaks but I could be wrong. I'll have to check again |
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Do that.
If everything looks good, try resetting the ECM to force it to relearn everything.
Between the battery and C500 connector is an ECM power connector.
Open it up, wait a few seconds, then plug it back in.
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Addition1291
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SEP 18, 05:39 PM
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I went and tested the MAP sensor and it passed. I reset the ECM too like you suggested. I couldn't find any vacuum leaks.
I should add that this problem only happens on the first drive of the day. If I drive it in the morning it will run like a potato until I park it and when I get back in later it will run just fine. Any subsequent drives and it will still run well but that first one of the day always has issues.
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fierosound
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SEP 18, 06:55 PM
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| quote | Originally posted by Addition1291:
I should add that this problem only happens on the first drive of the day. If I drive it in the morning it will run like a potato until I park it and when I get back in later it will run just fine. |
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Check your Coolant Temp Sensor (CTS) with a multi-meter.
It may be reporting a wrong temperature to the ECM.
On a cold engine, both the MAT and CTS should read about identical resistance.
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Addition1291
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SEP 19, 07:56 PM
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Tested the ECT. It failed hard. Looks like it is completely fried. I ordered a new one. I'll post an update once its installed.
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fierosound
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SEP 19, 11:12 PM
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| quote | Originally posted by Addition1291:
Tested the ECT. It failed hard. Looks like it is completely fried. I ordered a new one. |
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Hope they send you the correct Coolant Temp Sensor for ECM (on the left).
 [This message has been edited by fierosound (edited 09-20-2019).]
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Addition1291
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SEP 19, 11:44 PM
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Yeah I made sure to get the right one. I actually just got a gauge sender and installed it today because a previous owner had installed some kind of weird bootleg kind that came with its own single wire gauge which of course broke.
I actually used the old gauge sender as a temporary plug for the ETC while I wait for the new ETC to come in.
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Addition1291
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SEP 23, 03:27 PM
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Put in a new ECT. No change.
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fierosound
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SEP 23, 04:35 PM
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| quote | Originally posted by Addition1291:
Tested the ECT. It failed hard. Looks like it is completely fried. I ordered a new one. I'll post an update once its installed. |
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ODD that the ECM didn't report an ALDL error code if this is fried.
| quote | Originally posted by Addition1291:
Put in a new ECT. No change. |
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But maybe explains why there's no change...
Does Check Engine light come on as engine starts to stall? Any new codes?
I'm starting to wonder if there's a fault with the ECM.
This might be hard to track down without live sensor data from ALDL.
Just had to change ECM in my 87 GT for similar reasons.
Because cold start idle was awful. Engine would stall, then I would restart and stall again etc.
Was watching sensor data with TunerPro on laptop and saw ECM thought engine was "warm" (38C) even when cold.
On 3rd Key Off/Restart, engine temp would suddenly read correct (14C) and everything would be fine.
I had a spare ECM that I swapped in and no problems since.
I think I have a "cold solder joint" on the ECT input circuit on mainboard in the ECM I had in the car.
Most likely where pin C10 is soldered to the board itself. Haven't checked that yet though...[This message has been edited by fierosound (edited 09-23-2019).]
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