Idle logic.

[mrfixiter]

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.

[Gloyale]

Perhaps a TPS not adjusted correct?

 

(throttle position sensor)

[Fairtax4me]

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.

[mrfixiter]

 

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.

[4flat4s]

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.

How do you test the Idle Control Valve? Is there a baseline value to go on?

[Fairtax4me]

How do you test the Idle Control Valve? Is there a baseline value to go on?

How bout year and model?

Testing it is kinda useless. These either work or they don't. Checking resistance will only tell you of the coil inside the valve is bad. They're much more likely to get coked and sticky.

 

There are plenty of reasons for idle problems that are not related to the idle control valve, and there are several reasons you can get codes for the Idle control that are due to problems not related to the valve.

 

What problem are you having, and/or which codes?