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High Speed Idle


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24 replies to this topic

#1 cx20

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Posted 07 October 2003 - 11:31 AM

What RPM is normal for the high speed idle? Mine starts around 1800 RPM and if you gas it or take off driving it climbs up to 2600 to 3000 RPM. It seems pretty high and makes it a little tricky to drive unitl it warms up (2-3 mins). I did replaced the TPS last week. Before that it would go to 3000 RPM as soon as it was started cold and then it would drop to normal after a few minutes. The old TPS had an overall lower resistance than the new one if I remeber correctly, but it did not have any bad or dead spots. Any suggestions?

#2 frag

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Posted 07 October 2003 - 11:38 AM

Certainly is much to high. My idle speed never goes higher than around 1500 even on the coldest morning and then goes down to 700 rpm very rapidly.
Are you sure the throttle or throttle cable is not sticking or binding? Though it could be many other things.

#3 PAezb

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Posted 07 October 2003 - 11:55 AM

Did you adjust the rotation of the TPS so that the voltage between closed and full throttle changes between .5 and 5 volts (I believe that's the range). You might also want to check the IAC (Idler Air Control) unit - should be located near the throttle body and the TPS. It too has a "x" amount of degree rotation to set it right - I'm not sure how to measure it's operation but I do know it can affect RPM's, especially when the engine is cold.

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#4 Legacy777

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Posted 07 October 2003 - 05:06 PM

First make sure tps is fine.

Other issue might be the idle air control valve.

#5 cx20

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Posted 08 October 2003 - 11:29 AM

I thought that was high. I do idle about 700-800 RPM after warm up. It just cold starts that are a problem.

The TPS was not adjustable. The screw holes were not slotted. It just went on and would not rotate. I assumed it was different from the ones referred to in TPS posts I found here.

I will check the cable to see if it is sticking or dragging.

I did not think about the IAC. I will look at it next. Is there anything I should do or know before pulling it off? Tests?

Thanks for the help!

#6 Legacy777

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Posted 08 October 2003 - 05:22 PM

The IAC on the newer models are integrated into the TB, and are a plunger type device. Carbon can build up on the device and cause it to stick and you can get the high idle. All you really need to do is take it off clean the plunger and the hole up with some cleaner, and put it back on. We did that for my buddy's 99 RS. When cold he would get irratic very high idle problems.

It hasn't been cold enough in houston yet to see if it actually fixed the problem though......

#7 cx20

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Posted 08 October 2003 - 06:31 PM

I took off the IAC and cleaned it. It did not look or seem carboned enough to cause any problems. It was not a plunger type though. It was a roller type? It was right on top the of the throttle body. I will see in the morning if it helped any.

#8 frag

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Posted 09 October 2003 - 08:21 AM

777, what kind of cleaner did you use?

#9 cx20

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Posted 09 October 2003 - 11:27 AM

I removed the IAC and sprayed it with Gumout Choke & Carb Cleaner and worked it with a screw driver. I let it dry before reinstalling. I did not drive it today, but I did start it this morning. It went straight to 2900 RPM for about 3 secs and then dropped to 1800 RPM. I gassed it a couple times and it stayed at 1800 RPM idle. It did not climb as it has been. This is different from what it has been doing. I am going to see if it does the same tomorrow. My wife did drive it last night after I cleaned the IAC, so I do not think the few secs of 2900 RPM idle were do to left over cleaner in the IAC.

#10 1 Lucky Texan

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Posted 09 October 2003 - 12:39 PM

You may need to reset the ECU since you're rerporting a significant change in behavior now. The computer may have 'learned' an incorrect setting.


Carl
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#11 cx20

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Posted 09 October 2003 - 03:17 PM

I assume removing the negative battery cable works. Is there any certain amount of time?

#12 Legacy777

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Posted 09 October 2003 - 04:51 PM

30 min should do

#13 cx20

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Posted 13 October 2003 - 11:25 AM

Well I reset the ECU and it did not do anything. I am still getting high idles when cold. It still gets to 2900 RPM as before. Could the throttle body itself need a cleaning?

#14 Legacy777

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Posted 13 October 2003 - 04:59 PM

No, I doubt TB would be the issue. From personal experience, cleaning the TB caused a high idle.

As for the next step.....not sure, you may need to have it professionally diagnosed or get an OBD2 scanner to see if the IAC valve or other sensors are within specs.

#15 jcniest5

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Posted 13 October 2003 - 07:45 PM

(Edited: Oops, not sure if the 2.5L is like the 2.2L or not so this may not apply to you at all)

Not sure and I haven't try it on mine, but have you try loosening the screw to the left of the throttle body yet? Perhaps it may help.

#16 Legacy777

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Posted 14 October 2003 - 07:45 AM

Do not touch the throttle stop screw. That's a big no-no. The TB's are bench flowed to allow a certain amount of air past the throttle plate. Adjusting that screw throws things out of whack. Sure it may reduce your idle, but that's not fixing the problem. That would fixing the symptom, not the cause, and when you do that, you can really mess things up when the actual cause creates more problems, which may or may not be related to the that cause, or because you tried to fix the symptom.

#17 cx20

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Posted 14 October 2003 - 04:06 PM

Well, I think it is getting worse. Today the idel was very irradict even after warm up. It will idle steady for a little while then jump up a couple hunderd then drop to about 500 RPM and back up tp 900 RPM. It even was climbing up 2800 RPM after driving 15 miles at 65+mph. What ever it is maybe it will trip a code soon. Thanks for all the info.

Is there any way to test the IAC? Everything seems to keep point at it.

#18 Legacy777

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Posted 14 October 2003 - 04:45 PM

Well.....I've looked at the fsm info for the 2000 legacy....and they just tell how to remove and install the iac valve......

With that car, and the fact everything is electronic, you are going to need to diagnois it from the computer, which means taking it somewhere, or buying the scan tool/software to do it yourself.

Right now, I honestly wouldn't waste any more effort and time doing anything else.

#19 diga

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Posted 19 October 2003 - 09:08 AM

Try to use this info: http://www.geocities...leshoff/IAC.htm

But I do not know is it correct or not. I have not tried yet.

Egidijus
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#20 Setright

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Posted 19 October 2003 - 11:30 AM

Erratic idle speed sounds like IAC.

I am surprised Josh hasn't suggested the coolant temp sensor - he always seems to do so with this sort of problem, so I thought I'd bring it up. :D

#21 cx20

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Posted 24 October 2003 - 06:43 PM

Well I do not think it is the IAC. I pulled the wires off during high idle and it dropped down to normal warm idel of 800 RPM. However, I did notice something else today. I went out and started my subie (big frost this morning) and was letting it idle. It did not idle extra fast as usual just around 1700RPM. I had to take the trash out and when I walked back past the car the radiator fan was runnning. I looked at the temp gauge and it had barely moved. Does the coolant temp sensor control the fan? Is it normal for the fan to run for a few seconds at a time when the motor is cold? The fan kick on an off a couple times and only ran for about 4-5 secs each time. The temp gauge seems to work okay. Does it get it's signal from the coolant sensor or does it have it's own sensor? Thanks for all the help.

#22 Legacy777

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Posted 24 October 2003 - 07:16 PM

First of all....did you have any of the HVAC controls on? If the A/C or defrost is on, it will kick the fans on.

There are two temp sensors. A single wire sensor for the dash, and a two wire sensor for the ECU.

It really sounds like the sensor is bad, and it's telling the ECU the engine is cold, when it's really not. So you are getting an extremely rich mixture, and the high idle. The sensor is like 20 bucks from liberty subaru www.newsubaru.com

#23 cx20

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Posted 24 October 2003 - 07:46 PM

I had the defrost running. Is there an easy way to check the sensor? It should just be a variable resistor. What would be the cold ohm value and a hot ohm value? I checked and Autozone also has the sensor for $20 also.

#24 Legacy777

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Posted 25 October 2003 - 08:53 PM

even when you test them, they may not show bad. For 20 bucks, just replace it.

#25 cx20

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Posted 03 November 2003 - 12:33 PM

Well, I replaced the coolant temp sensor and seems to have fixed the problem. It has been okay for a couple days now.

Thanks for all the help.




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