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Very High Idle only when it's cold outside by jschmidt95
Started on: 12-05-2014 02:07 AM
Replies: 6 (493 views)
Last post by: 1MohrFiero on 12-11-2014 06:57 AM
jschmidt95
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Report this Post12-05-2014 02:07 AM Click Here to See the Profile for jschmidt95Click Here to Email jschmidt95Send a Private Message to jschmidt95Edit/Delete MessageReply w/QuoteDirect Link to This Post
**I have done a very thorough search on the entire forum+Archives before creating this thread, Promise**

Hi All
My car is a 1986 Fiero SE 2.8l V6 110,000 miles Near stock. Cat Deleted w/ no tuning done (Mechanic told me this wouldn't be the problem though)

Since I've had it the car(about a year now) I have had this problem.

When it is warm outside (upwards of 50*F) the car starts right up, idles at 1300RPM and drops down to a comfortable 900RPM after about 20 seconds, just as it should.
However, when it is less than 50*F The idle is very high, between 1900 and 2500RPM and stays that temperature until The engine is at operating temp (Usually about 10 minutes on the freeway)
While the idle is this high, there is a SIGNIFICANT loss in power, I stall out maybe one in 5 times i take off from a light when it's this high. The problem is directly linked to the outside temperature.
No Check Engine Light during this problem EVER. (it does turn on for the lamp check right before you start the engine) and no codes are stored on the ECM.

What I have done:
Checked for EGR tube leaks at the shop -none
checked torque on all intake bolts -good
replaced MAT and MAP sensors with genuine ACDelco parts
Replaced all the vacuum lines with Rodney's stainless steel ones (After I did this, my cruise control started working again)
Checked for vacuum leaks with new Vacuum tubes -none
Replaced IAC valve and allowed the ECM to calibrate
replaced O2 sensor with ACDelco Part
Replaced Spark plugs, distributor cap and rotor and will be replacing wires this weekend.
My dad and I will be replacing the Distributer O-Ring this weekend, and we will be double checking the timing before

When I have the air intake hose off, I can put my palm over the throttle body opening and the engine will get sluggish for 2 seconds and then stall, I think this is normal.
I tested the TPS with an Ohm meter, but haven't replaced it yet.

This wouldn't bother me so much except every time i start from a stop, I feel like I am wearing out my clutch for no good reason b/c the idle is so high.

On an unrelated (I think) note, I have been having some cold weather electrical problems, but I think its because snow finds its way into the battery area and causes something to ground because it doesn't happen when there isn't snow back there.

I'm going to try and film a short video explaining this tomorrow

Again, Thanks in advance!

[Edit to add Cat Delete]

[This message has been edited by jschmidt95 (edited 12-05-2014).]

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f85gtron
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Report this Post12-05-2014 07:01 AM Click Here to See the Profile for f85gtronSend a Private Message to f85gtronEdit/Delete MessageReply w/QuoteDirect Link to This Post
Your list doesn't include the coolant temperature sensor for the ecm (the one below the thermostat housing, pointing horizontal at the passenger side strut tower). Between that and the mat sensor on the air cleaner housing, that's what brings your open loop idle up. ....other than vacuum leaks.
Ron
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Gall757
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Report this Post12-05-2014 09:24 AM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
coolant temp sensor.....(ECM temp sender)

[This message has been edited by Gall757 (edited 12-05-2014).]

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jschmidt95
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Report this Post12-05-2014 10:38 AM Click Here to See the Profile for jschmidt95Click Here to Email jschmidt95Send a Private Message to jschmidt95Edit/Delete MessageReply w/QuoteDirect Link to This Post
oohh cool. thabks so much. i'll pick up a new one this week, hopefully this fixes my problem
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theogre
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Report this Post12-05-2014 11:27 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
Maybe Look for Vac leak that open up when engine is cold.
Some spots listed here... See my Cave, Vac Leaks


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[This message has been edited by theogre (edited 12-05-2014).]

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armos
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Report this Post12-07-2014 11:14 AM Click Here to See the Profile for armosSend a Private Message to armosEdit/Delete MessageReply w/QuoteDirect Link to This Post
Your car is dropping to the normal 900rpm idle when it warms up, so it's not a vacuum leak unless it's a leak that only happens when it's cold. The fact that you can stall it by blocking the throttle also reinforces this. I'm assuming you did that experiment with it cold.

When the ECM detects a low coolant temperature, it will increase the opening of the IAC, causing it to idle faster. It does this more aggressively than a modern car would. I think up to 2000rpm is normal, but 2500rpm may not be. However, the range of the high idle might be partly influenced by the position of the throttle adjustment screw, so that could explain variance from one car to another. Personally I've never seen it go higher than 2000.
It does seem like it's taking too long to settle down. Does the temperature gauge show that it's just taking a long time to warm up?
In case you don't already know, the sender that controls the dashboard temperature gauge is separate from the one that talks to the ECM. The dashboard reading is not necessarily what the ECM is seeing.

Perhaps the coolant temperature sensor is giving a skewed reading, reporting a colder temperature to the ECM than reality. This could be caused by a bad sensor, which you've said you're going to try replacing. A skewed reading could also be caused by high resistance in the wiring. I think that's unlikely though, because this would have less effect when cold and more effect when hot, which is the opposite of where you're seeing noticeable issues.

If you want to test your CTS before replacement, it is possible to do that by measuring it's resistance. I don't have the data handy but if you look around, there are charts showing what resistance corresponds to a given temperature. This will tell you if the sensor itself is working correctly.

I think it's very likely that the temperature reading to the ECM is fine. Since you have a driveability problem when cold, it may be idling faster purely for that reason. When the engine stumbles to a near stall, the ECM will raise the idle, then after a few seconds it will begin to gradually back it down. If it keeps stumbling then the idle may keep jumping up because of it. The idle speed may be a side effect, with the root cause being whatever is causing it to idle poorly when cold. Unfortunately, that could be a lot of things, because a car will almost always find it easier to idle when warm vs cold.

If you're computer inclined, you might find it interesting to hook up a laptop and use WinALDL to watch the ECM parameters (including sensor values) as it runs. This requires an ALDL cable, I won't get into that here but there should be info on the forum about how to make or buy one.

[This message has been edited by armos (edited 12-07-2014).]

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1MohrFiero
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Report this Post12-11-2014 06:57 AM Click Here to See the Profile for 1MohrFieroSend a Private Message to 1MohrFieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
So did the CTS help?

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