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88 C4 idles too fast. Any suggestions?

 
Old 02-17-2019, 08:24 PM
  #21  
aklim
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Originally Posted by CorvetteRules View Post
If you want to eliminate the CTS unplug it and see if the idle is lower. Although I can tell you when my CTS was bad it showed up as a code 15 when scanned.
If the temp is correct, what would happen?
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Old 02-17-2019, 08:34 PM
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Originally Posted by aklim View Post
If the temp is correct, what would happen?
Nothing, but if OP wants to prove to himself it isn't the CTS it is a quick and easy way to do it.
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Old 03-12-2019, 07:41 PM
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Originally Posted by aklim View Post
When you had everything but the motor off at operational temp, how many IAC counts?
144 counts. When ohmed, the coils of IAC read about 59 ohms on each. When I run a test light to ground, each lead of the IAC connector read as hot, light came on.
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Old 03-12-2019, 07:44 PM
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Originally Posted by jrobinsonsrr View Post
144 counts. When ohmed, the coils of IAC read about 59 ohms on each. When I run a test light to ground, each lead of the IAC connector read as hot, light came on.
Way too many. You don't have enough air coming in for the condition. Is the timing at 6 degrees?
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Old 03-12-2019, 07:51 PM
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Originally Posted by xrav22 View Post
Well I would think that if everything else was working then the idle procedure will help set the idle.
You have to start somewhere. Then see if any codes come up.
I had the timing checked, it is correct. I did the set idle procedure in SM and when I unplugged the distributor lead to ECM as directed the idle returned to 400 rpm as called for in SM. That tells me that the minimum idle is correct and that the ECM is speeding up the motor. Hooked everything backup and idle goes back to 800 rpm. I am back to scratching my head. Nothing running but motor, in neutral.
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Old 03-12-2019, 07:53 PM
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Way too many counts or ohms? Timing is at 6 degrees.
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Old 03-12-2019, 07:55 PM
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I am thinking of pulling IAC and see if it is set correct using the settings in SM for installing a new unit. Thoughts?
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Old 03-12-2019, 07:58 PM
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Originally Posted by jrobinsonsrr View Post
Way too many counts or ohms? Timing is at 6 degrees.
Way too many counts. Usually it should be about 20 or 30. What is the command idle at this point?
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Old 03-12-2019, 09:44 PM
  #29  
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Originally Posted by jrobinsonsrr View Post
I am thinking of pulling IAC and see if it is set correct using the settings in SM for installing a new unit. Thoughts?
I would try to reset it using IAC counts and forget the FSM method. The FSM way assumes you have a perfect system except that the throttle blades are too far in or out.

I would first see what the ECM thinks the idle should be. Check out what the CTS is saying VS the infrared thermometer. Also see what the IAT is reading VS the thermometer
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Old 03-13-2019, 01:15 PM
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Originally Posted by aklim View Post
I would try to reset it using IAC counts and forget the FSM method. The FSM way assumes you have a perfect system except that the throttle blades are too far in or out.

I would first see what the ECM thinks the idle should be. Check out what the CTS is saying VS the infrared thermometer. Also see what the IAT is reading VS the thermometer
Scanner only shows desired idle and actual idle. Desired is about 200 lower than actual. By checking the CTS, are you thinking that the ECM thinks the engine is cooler than actual? Does the scan tool allow you to change the output?
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Old 03-13-2019, 01:23 PM
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Originally Posted by jrobinsonsrr View Post
Scanner only shows desired idle and actual idle. Desired is about 200 lower than actual.

By checking the CTS, are you thinking that the ECM thinks the engine is cooler than actual? Does the scan tool allow you to change the output?
So the actual idle is higher than desired? Is the actual really from the ECM or the tach?

I was wondering if the CTS was correct. IOW, it might be 150 when the CTS thinks it is 100. I try make sure the CTS is about the same as the ECM. No you cannot change the output since there is no way and even if you could, it wouldn't' be desirable to try fool the ECM unless it is a last resort.

I'm wondering if your tach is accurate.
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Old 03-13-2019, 08:42 PM
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The tach agrees with an external tach so I believe it is right. And the higher idle makes the car creep forward sitting in drive at a light. I rechecked the IAC count with engine warm and idling and it reads about 70 counts. My IF gives me about the same temp as the scanner and display so I believe the coolant temp sensor is reading correctly. I do know that the thermostat is a 160 deg unit and I think the book calls for 180 or higher but I am not sure that would make a difference.
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Old 03-16-2019, 09:37 PM
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Originally Posted by jrobinsonsrr View Post
I know that the thermostat is a 160 deg unit and I think the book calls for 180 or higher but I am not sure that would make a difference.
There you go. Yes it matters. What engine temperature is the scanner reading? The number in degrees, not "it's reading normal".
Your idle speed will ramp down as the engine warms up.
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Old Yesterday, 10:54 AM
  #34  
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Originally Posted by Benny42 View Post
There you go. Yes it matters. What engine temperature is the scanner reading? The number in degrees, not "it's reading normal".
Your idle speed will ramp down as the engine warms up.
If the idle ramps up or down, isn't that the desired idle? The ECM has decided on the idle speed to be say 600 based off the temperature it sees. But what would make it 800 if the ECM thinks it should be 600?
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Old Yesterday, 01:06 PM
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Originally Posted by aklim View Post
If the idle ramps up or down, isn't that the desired idle? The ECM has decided on the idle speed to be say 600 based off the temperature it sees. But what would make it 800 if the ECM thinks it should be 600?
Yes it should, but we still don't know why he has 144 IAC counts when the ECM is commanding 600 rpms while its idling
at 800.
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Old Yesterday, 03:53 PM
  #36  
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Originally Posted by Benny42 View Post
Yes it should, but we still don't know why he has 144 IAC counts when the ECM is commanding 600 rpms while its idling
at 800.
Could we start with cleaning the TB passages and resetting it using IAC counts?
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