Fixed my idle problem.
Thread Starter
Melting Slicks
Joined: May 2001
Posts: 2,161
Likes: 0
From: Tyler TX
Fixed my idle problem.
I posted this weekend that my rpm's at idle shot up to 1800RPM during a trip. Using the tips on how to reset the IAC motor and the Tech Tip on how to set the idle speed on an early C4, I was able to get my idle speed down to 550. Even when I first got the car it idled at 900RPM, so now I've got it set just right. Now I'll probably have less overheating problems now that the idle is half of what it was.
Safety Car
Joined: Oct 1999
Posts: 4,679
Likes: 2
From: Honolulu HI
Re: Fixed my idle problem. (91-Z07Coupe)
91 Z07,
I don't remember from your previous posts if you have taken off the throttle body and removed the IAC and given both a thourough cleaning. If you haven't, you might try that and then reset the idle again. It is a real simple job. Another thing I read recently was to pull the fuse on the ECM for 30 seconds. Good luck.
Aloha,
Larry
[Modified by Larry Mackey, 5:39 PM 8/28/2001]
I don't remember from your previous posts if you have taken off the throttle body and removed the IAC and given both a thourough cleaning. If you haven't, you might try that and then reset the idle again. It is a real simple job. Another thing I read recently was to pull the fuse on the ECM for 30 seconds. Good luck.
Aloha,
Larry
[Modified by Larry Mackey, 5:39 PM 8/28/2001]
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Re: (scorp508)
Below 100 deg F your engine runs open loop (no ECM altering a/f or timing or idle from sensor readings). After 100 deg, your engine runs closed loop (ECM uses sensor data to control engine conditions).
Burning Brakes
Joined: Aug 2001
Posts: 1,238
Likes: 0
From: walled lake MI
Re: (scorp508)
mine idles at about 1100 at cold, then about 700-800 warm too.
by the way, when the engine is cold, the operating mode would be "open loop", indicating that the a/f mix is controlled by an educated guess by the ecm usually using throttle/rpm/coolant temp. when the engine warms up, the "closed loop" kicks in, and the mixture is also controlled from feedback from the O2 sensor in addition to the open loop calculations.
idle speed would be considered constantly "closed loop," meaning that the ecm controlls idle speed by using the rpm readings as feedback. the reason why it idles high at startup is because the target idle speed, as determined by the ecm, is calculated from usually coolant temp. cold=high, warm=low.
as for the idle problem, i agree that a thorough cleaning of the idle air control circuit is probably good thing to do. the idle control valve is just that, a valve, and it is known to stick. in that case you'd probably want to replace the valve.
good luck! :cheers:
by the way, when the engine is cold, the operating mode would be "open loop", indicating that the a/f mix is controlled by an educated guess by the ecm usually using throttle/rpm/coolant temp. when the engine warms up, the "closed loop" kicks in, and the mixture is also controlled from feedback from the O2 sensor in addition to the open loop calculations.
idle speed would be considered constantly "closed loop," meaning that the ecm controlls idle speed by using the rpm readings as feedback. the reason why it idles high at startup is because the target idle speed, as determined by the ecm, is calculated from usually coolant temp. cold=high, warm=low.
as for the idle problem, i agree that a thorough cleaning of the idle air control circuit is probably good thing to do. the idle control valve is just that, a valve, and it is known to stick. in that case you'd probably want to replace the valve.
good luck! :cheers:
Team Owner
Joined: Mar 2000
Posts: 83,381
Likes: 87
From: Boston, MA
Re: (jfb)
Below 100 deg F your engine runs open loop (no ECM altering a/f or timing or idle from sensor readings). After 100 deg, your engine runs closed loop (ECM uses sensor data to control engine conditions).
Whoops, sorry, backwards.
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