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| Incosistent idle on an '84 after IAC replacement (Page 1/1) |
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stapler8
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SEP 19, 04:34 AM
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This is what my normal idle looks like from cold to hot:
30 seconds after starting a smooth idle at ~1200RPM
About 2 minutes of idling at ~2500 RPM while it warms up
Slowly going down to about ~1000 RPM over the next 5 minutes of light driving/idling.
Then when it gets to just about the first notch on my temp gauge, the idle goes wonky. It'll rev up to ~1700 RPM for a second, then quickly drop down to ~400 RPM before it lugs for a bit and rises back up to 1700. Sometimes it drops to zero and stalls the car.
Now here's the fun bit. If I do some highway driving, maybe 30 minutes or more at 70-75 MPH, my temperature increases slightly past the first notch, then it idles consistently at 1000 RPM until I get back in the city, the engine cools down, and I'm back to the weird idle.
It's making it hard to start off without stalling or giving it too much gas, as well as making my shifts rougher. Thermostat and IAC were replaced recently, but it started before the new thermostat was in.
I've heard something about jumping pins, but I'm not entirely sure what pins or where they are. Any help would be much appreciated.
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edfiero
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SEP 19, 08:27 AM
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It would be good if you could get a scanner on it and read the data form the ECU in real time.
There is more than 1 temp sensor, one for the dash gauge and one for the computer. It almost seems as if the temp gauge to the computer could be sending whacky info.
(Having a fast idle (1500-2000) is normal at a cold start, but after the cooland starts to warm, you should be down to 1000rpm (with a manual tranny)
It would also be good to make sure the Throttle Position Sensor is giving the computer the correct inputs as well.
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stapler8
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SEP 19, 08:31 AM
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I have a very basic toolset, so anything like a scanner is beyond my capabilities.
It does idle around 1000RPM, but once it gets fully warmed up then the bad idle starts.
How would I check the TPS?
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fierosound
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SEP 19, 11:43 AM
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2.5
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SEP 19, 11:43 AM
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| quote | Originally posted by stapler8:
Now here's the fun bit. If I do some highway driving, maybe 30 minutes or more at 70-75 MPH, my temperature increases slightly past the first notch, then it idles consistently at 1000 RPM until I get back in the city, the engine cools down, and I'm back to the weird idle.
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What do you refer to as the first notch? Your Fiero should hit 180 or 195 F (depending on which Tstat you chose) within a short time of driving any speed.[This message has been edited by 2.5 (edited 09-19-2019).]
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stapler8
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SEP 19, 11:49 AM
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Fierosound:
That was installed by my local mechanic. I would imagine that he did so, he's pretty good at looking these things up when he works on my car. Could that cause an unstable idle? After looking in my Haynes manual, the symptoms I've got are pretty much the same as a broken TPS.
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2.5:
https://upload.wikimedia.or...Pontiac_Fiero_SC.JPG (not embedding the image, it's massive)
That's not my picture, but you can see what I mean by the first notch, right under where the needle is. It's a 195*F thermostat. Takes about 5 minutes to warm up with the slower driving around here.[This message has been edited by stapler8 (edited 09-19-2019).]
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fierosound
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SEP 19, 12:16 PM
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| quote | Originally posted by stapler8:
That was installed by my local mechanic. I would imagine that he did so, he's pretty good at looking these things up when he works on my car. Could that cause an unstable idle?
After looking in my Haynes manual, the symptoms I've got are pretty much the same as a broken TPS.
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I'd still try resetting the ECM by disconnecting/reconnecting it's power.
Then at some point after driving, if problems persist, see if there's any Engine Codes.
http://www.fiero.nl/cgi-bin/main.cgi?ECMCodes[This message has been edited by fierosound (edited 09-19-2019).]
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