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Guest Message by DevFuse

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Idle logic.

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3 replies to this topic

#1 mrfixiter


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Posted 01 September 2014 - 11:46 AM

I have a 1997 GT Legacy Wagon, m/t, 2.5l. The problem which has been happening for as long as I can remember (since the car was a few years old) is that when I first start the car in the morning, the idle speed is close to the 1,700-2,000 rpm range. As I drive sometimes it settles down quickly to where it's supposed to be at 750 rpm. The glitch that I have found is that sometimes the idle will "stick" at about 1500 rpm until I come to a complete stop for at least 5-10 seconds. Then the idle always returns to normal. I remember taking it to the dealer when the car was still in warranty but  I was told that they couldn't duplicate the problem. Since there is not much traffic where I live I can drive for 20 minutes without coming to a complete stop. When that happens, it's almost like driving with the cruise control on but of course the cruise control is not on. I live in Los Osos, CA which has a very temperate climate and this high-idle-until-stopped happens all year long. The temperature gauge always parks itself in the same place when the car warms up. My question is: Is this normal?


One more piece of information. I do remember that there was a time a few years ago that it would never return to the normal idle speed even after stopping for a few seconds. Coincidentally, I had to take the car in for a smog check and when I drove away, the problem was fixed. I did remember seeing from a distance that the mechanic sprayed something in the vicinity of the throttle body assembly so I was wondering if it was sticking. But now the original problem has returned to where I have to come to a complete stop before the idle goes back to normal. By the way, the idle will not go back to normal if I just coast down the street with no foot on the gas.


Thanks for your reply. :)

#2 Gloyale


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Posted 01 September 2014 - 11:53 AM

Perhaps a TPS not adjusted correct?


(throttle position sensor)

#3 Fairtax4me



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Posted 01 September 2014 - 10:17 PM

The ECU will hold idle up some when coasting but should only be around 900-1000 rpm.
The highest high idle you should ever get is 1750 rpm, but that won't be unless its well below freezing outside.
Idle higher than that on a warm day says either the throttle is partially stuck open, or the Idle Control Valve is misadjusted.

#4 mrfixiter


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Posted 02 September 2014 - 10:54 AM

Idle higher than that on a warm day says either the throttle is partially stuck open, or the Idle Control Valve is misadjusted.

That all makes sense but how would that explain why sitting at a red light for about 5-10 seconds sets the idle speed back to normal for the remainder of the drive?


Thanks for your reply. :)

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