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Old 04-12-2021, 03:32 AM   #1
coltkirch
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Member#: 523570
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Post Rough Idle when Radiator fans turn on

I have an 02 WRX that has a very rough idle and sometimes stalls whenever the radiator fans turn on. Whether it is from coolant temp or manually with A/C toggle. I have already cleaned my Idle air control unit and it appears to be working when I test if the RPM's spike with the AC on. It does...

Another thing is that it won't rough idle when the hood is up. So if radiator fans are on and the hood is up, it will be fine. There are no hoses that are getting smashed by the hood either so I am at a loss at what the heck is the real cause of this. I don't wanna be replacing alternators and other units that are not probable causes. any suggestions would be great.
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Last edited by coltkirch; 04-12-2021 at 03:35 AM. Reason: Mistyped the title
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Old 04-12-2021, 09:03 AM   #2
ProjectWhiteWrx02
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Hey, Welcome. I have an 02 and i'm also experiencing coolant issues granted mine is the radiator
#1 Have you checked if you have air in the cooling system? (You can uncap the expansion tank cap and just squeeze the main top radiator hose to see if it bubbles or coolant levels drop.)
#2 Have you tested the heater on the car to see if it needs to be flushed?(heater performs very poorly on max settings)
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Old 04-12-2021, 02:32 PM   #3
Jedi03
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would recommend also do some de-carboning of the engine eg seafoam through intake hose/brake booster, i also use ATF in my fuel regularly to help combat it...thought process is that if the engine is able to perform properly it should help with any extra load on it...maybe make sure engine mounts are in good shape too
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Old 04-13-2021, 03:43 PM   #4
coltkirch
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Quote:
Originally Posted by ProjectWhiteWrx02 View Post
Hey, Welcome. I have an 02 and i'm also experiencing coolant issues granted mine is the radiator
#1 Have you checked if you have air in the cooling system? (You can uncap the expansion tank cap and just squeeze the main top radiator hose to see if it bubbles or coolant levels drop.)
#2 Have you tested the heater on the car to see if it needs to be flushed?(heater performs very poorly on max settings)
Would air in the cooling system cause it to rough idle like that though? Since the rough idle only occurs when the fans turn on, I feel like it would be more towards electrical-based units or intake components? I don't know maybe I'll try and burp the system and see what happens.
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Old 04-14-2021, 04:50 PM   #5
umscooby
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Battery/alternator.
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Old 04-14-2021, 11:31 PM   #6
AliBenn
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^^^^nailed it
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Old 04-20-2021, 05:52 PM   #7
runner19
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The alternator is dragging the engine rpm down. It may be the alt bearings(unlikely).

unplug alt, cause fans to run, see if it happens, if not alt needs a rebuild.

Spin alt pully by hand, not it is does not spin true.

Does Idle drop. You need to bump it up.

After market belts can also cause this.
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