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Temp high idle issue
Topic Started: Jan 11 2011, 05:10 AM (1,947 Views)
honestabe


My 95 base model 1.0 idles high when I let off the gas and put the trans in neutral. After a few seconds of the car in neutral the idle drops down to a normal level. Is this common or is there something I should be repairing?

Thanks,
Adam
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Bad Bent
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Facetious Educated Donkey

The usual mantra on high idle is vacuum leak. Perhaps the beginning of a major leak, maybe the PCV valve is sticking open. I recommend changing the vacuum hoses, if you have not already done so. To test a hose, you can bend the hose to see if it has any cracks. To replace, start with 5' of 1/8" hose and replace one at a time.

Next test would be spraying carb. cleaner or starting fluid around the hoses and gaskets. When your idle goes up you found your leak.

I gather there is no Check Engine Light.

You can check for a sticking throttle plate also. This is where spraying the TB for leaks would clean it at the same time. :thumb
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slander
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An out-of-tune TPS will do that as well.
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honestabe


I just replaced the PCV valve recently, and the CEL is not on (although I did just have to clean my EGR valve due to a CEL). I haven't replaced my vacuum hoses, but I will probably do that today. At the worst it is cheap insurance and good maintenance. I also recently sprayed the TB with carb cleaner and it isn't sticking. I'll report back later with the results of doing as Bad Bent said to do.
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slander
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Did you also soak your TPS while spraying the TBI unit? Check to be sure there isn't a bunch of moisture in the TPS plug.
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honestabe


I couldn't even identify the TPS on this motor. But I did just replace the vacuum lines (they were toast) and changed my oil. I also sprayed some carb cleaner down my throttle body while it ran and it did seem to smooth things out a little. When I fill-up my gas tank next I'll do a Seafoam treatment.
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slander
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This is a spare manifold, with TBI unit and TPS still attached, sitting atop of another G10. Big circle is the TPS, second shows a ground. It wouldn't hurt to make sure the ground is nice and tight, but it doesn't necessarily pertain to the issues you're having. I repurposed an old picture.

Posted Image
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honestabe


So I completely forgot about this issue until tonight. I popped the hood and looked at the TPS, it's bone dry inside and out (although very dusty). The ground is also very tight. I haven't sprayed for leaks yet but I will try and do that tomorrow. As for adjusting the TPS, that's something too sensitive for me to feel comfortable messing with.
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honestabe


How would I verify that my TPS is out of tune anyways?
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zcrayfish
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honestabe
Feb 1 2011, 04:44 AM
How would I verify that my TPS is out of tune anyways?
Check the idle switch, pins A & B, this image is a good reference:

Posted Image

Here's a relevant thread.
http://geometroforum.com/topic/1341780

Checking pins C & D is a major waste of time, accurately measuring resistance on this part is next to impossible.
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honestabe


Thank you
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honestabe


Well I just replaced the coolant temp sensor on the suggestion of my dad who's a retired master mechanic and that seemed to fix the problem. I wish I had a tach so I could verify this.
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zcrayfish
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honestabe
Feb 3 2011, 08:28 PM
Well I just replaced the coolant temp sensor on the suggestion of my dad who's a retired master mechanic and that seemed to fix the problem. I wish I had a tach so I could verify this.
You can verify that the computer controlled idle is working without a tach...

On models with IAC solenoid valve (ones with a vacuum diagram like this) start the car, remove the silencer/air chamber from the IAC solenoid valve... At fast idle (car cold) it should make a very loud thud-thud-thud-thud-thud sound... At normal idle (car warm) it should make very little noise with the silencer removed.

On models with ISC motor that pushed the throttle plate open (TBI has a black box attached to it looks like this) ... At fast idle the plunger should be pushing the throttle slightly open... At warm, the plunger should not be pushing the throttle open (throttle should be resting on stop screw)
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honestabe


I was wrong, the temp sensor didn't fix my problem with my idle.

The tach just makes it easier to check my RPM's. I have the ISC motor. I'll check it tomorrow. So if the ISC motor is bad it will hold my throttle open temporarily when warm correct?
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Wobblybob


abe,

What did you ever find out about your ISC?

BTW, the FSM page (regarding setting the TPS) that zcrayfish posted on 2/1/11 is for a '92 and will not work on your '95. Your '95 TPS has 4 pins but only 3 are used: A,C & D (A is nearest the firewall). Instead of hooking your meter to A & B as shown, you need to hook it to A & C.

But what about your ISC findings?
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