Running too cool a problem ?
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 898
Likes: 1
From: Pearland Texas
Running too cool a problem ?
I've got an 180* thermostat and a TB bypass. My problem is that the needle does'nt get up to halfway on the temp gauge. (approx 180*) Soo, it doesn't idle down. It always runs like it cold idling at about 11-1200 RPM all the way to work. Its like cruise control. I've haven't seen a thread on this problem. Other than shoving debris in the radiator are there any ideas out there ? 
Le Mans Master
Joined: Mar 2004
Posts: 8,700
Likes: 298
From: Ft. Lauderdale Fl
You might want to do a search on this one as there is much written on this subject. I run in the low 170's on the highway for 25 miles each A.M., seven days a week with no ill effects so far. 133000 on the clock, 1996.
Team Owner
Joined: Jun 2001
Posts: 26,196
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From: Orlando FL
St. Jude Donor '08-'09
It just happened again yesterday, but was stuck at 1700 and was able to pull me home without touching the gas once I got up to speed
Safety Car
Joined: Jul 2004
Posts: 3,835
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.....ther are some posts relating to the "seting/re-setting" of the iac....
Melting Slicks
Joined: Jan 2002
Posts: 2,238
Likes: 4
From: Milan
I've got an 180* thermostat and a TB bypass. My problem is that the needle does'nt get up to halfway on the temp gauge. (approx 180*) Soo, it doesn't idle down. It always runs like it cold idling at about 11-1200 RPM all the way to work. Its like cruise control. I've haven't seen a thread on this problem. Other than shoving debris in the radiator are there any ideas out there ?
The stock table in the chip " Idle Engine Speed Vs. temp "
for a 1990 is:
-4°C = 1050 rpm
...
8°C = 950 rpm
20°c = 850 rpm
32°C = 800 rpm
...
56°C = 700 rpm
68°C = 650 rpm
from 80°C to 152°C = 600 rpm
180°F are about 76°Celsius so your car should be idle at 600 and it's considered fully warmed .
-Beppe-
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
temp
1. your gauge is lying to you
2. your egr might be sticking open when it's use is not required, adding too much carbon into your intake manifold
3. you might be adding air through a vacuum leak, raising the idle.
It is interesting to note, that on a fuel injected porsche, they add a calibrated leak to raise the idle when cold, then compensate for it by adding a little fuel.
Meaning:
if you have a vacuum leak, the IAC may be all the way closed trying to compensate for the idle RPM when warm.
2. your egr might be sticking open when it's use is not required, adding too much carbon into your intake manifold
3. you might be adding air through a vacuum leak, raising the idle.
It is interesting to note, that on a fuel injected porsche, they add a calibrated leak to raise the idle when cold, then compensate for it by adding a little fuel.
Meaning:
if you have a vacuum leak, the IAC may be all the way closed trying to compensate for the idle RPM when warm.
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Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 898
Likes: 1
From: Pearland Texas
Several months ago I did a fuel injector swap out. Even removed the intake manifold to fix an rear china wall seal leak. Started a thread about a mechanic who thought I had cracked intake, got lots of help on that. That never was the problem. All the vacuum lines are good, no leaks. I bought a new IAC and follwed Vaders instructions exactly. New CTS, I didn't replace the EGR at the time, could'nt get one quickly enough. At the time of the IAC reset I could get it to idle where it is supposed to. I'm looking at getting an infrared temperture sensor and get a reading that way.
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 898
Likes: 1
From: Pearland Texas
The coolant temp has nothing to do with idle speed at 180°F.
The stock table in the chip " Idle Engine Speed Vs. temp "
for a 1990 is:
-4°C = 1050 rpm
...
8°C = 950 rpm
20°c = 850 rpm
32°C = 800 rpm
...
56°C = 700 rpm
68°C = 650 rpm
from 80°C to 152°C = 600 rpm
180°F are about 76°Celsius so your car should be idle at 600 and it's considered fully warmed .
-Beppe-
The stock table in the chip " Idle Engine Speed Vs. temp "
for a 1990 is:
-4°C = 1050 rpm
...
8°C = 950 rpm
20°c = 850 rpm
32°C = 800 rpm
...
56°C = 700 rpm
68°C = 650 rpm
from 80°C to 152°C = 600 rpm
180°F are about 76°Celsius so your car should be idle at 600 and it's considered fully warmed .
-Beppe-
I thought thats what the CTS purpose is. Doesn't it tell the ECM to compensate for cold and warm. First you say it has nothing to do with the idle speed, then I see a chart and a quote" your car should be idle at 600 and it's considered fully warmed." Mine is at 1000 rpm. I will run it in the garage tonight and get it hot and watch idle speed. Will let you all know.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by coupeguy2001
It is interesting to note, that on a fuel injected porsche, they add a calibrated leak to raise the idle when cold, then compensate for it by adding a little fuel.
Originally Posted by RRT vette
Then check the TPS voltage for the high idle.
Originally Posted by Dads90
Originally Posted by conv90
The coolant temp has nothing to do with idle speed at 180°F.
The stock table in the chip " Idle Engine Speed Vs. temp "
for a 1990 is:
-4°C = 1050 rpm
...
from 80°C to 152°C = 600 rpm
180°F are about 76°Celsius so your car should be idle at 600 and it's considered fully warmed .
-Beppe-
The stock table in the chip " Idle Engine Speed Vs. temp "
for a 1990 is:
-4°C = 1050 rpm
...
from 80°C to 152°C = 600 rpm
180°F are about 76°Celsius so your car should be idle at 600 and it's considered fully warmed .
-Beppe-
RACE ON!!!
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 898
Likes: 1
From: Pearland Texas
I let it run for 30 minutes in the garage and it got up to 220* and the fans kicked in like normal. The idle dropped down to 900 rpm and stayed there. I did noticed it idled high on a restart. Will do a IAC reset tomorrow. Stay tuned.
Last edited by Dads90; Sep 8, 2007 at 07:03 PM. Reason: didn't finish
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
If the TPS has been moved to to send a voltage greater than the normal, the ECM would not know if the throttle plates are opened or not.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
idle
When the engine is restarted, it goes through a cannister purge, and after that is accomplished, the idle drops from 900 RPM down to 550.
Just for grins, check to see that the idle isn't being affected by the canister purge solenoid sticking open.
worth a try.............
Just for grins, check to see that the idle isn't being affected by the canister purge solenoid sticking open.
worth a try.............
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 898
Likes: 1
From: Pearland Texas
When the engine is restarted, it goes through a cannister purge, and after that is accomplished, the idle drops from 900 RPM down to 550.
Just for grins, check to see that the idle isn't being affected by the canister purge solenoid sticking open.
worth a try.............
Just for grins, check to see that the idle isn't being affected by the canister purge solenoid sticking open.
worth a try.............
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 898
Likes: 1
From: Pearland Texas
Doesn't my vette have an unadjustable TPS ? I did drill out the bottom hole so I could adjust it, after messing with it I saw a post about it not being necessary to adjust. So it sets unadjusted right now. May put my volt meter on it anyway.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Your right, the 90 TPS is not adjustable..........see what the volt reading is.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by RRT vette
Originally Posted by CFI-EFI
When the ECM commands a fast idle, the throttle, and therefore the TPS voltage, never changes. ECM commands and vacuum leaks don't move the throttle blades. TPS stands for Throttle POSITION Sensor.
Checking the TPS voltage, other than confirming that it is within the non-adjustable TPS standards and establishing that it is functioning properly, will prove nothing. Whatever the voltage, the computer accepts the lowest reading as closed throttle.
RACE ON!!!