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Tech Tips, Tech Questions / IAC control input
« Last post by Fierofool on March 08, 2025, 12:46:22 pm »The IAC isn't really a sensor in and of itself though it's function output acts as a sensor. What other sensor causes the IAC to react?
I have set the TPS to exactly 0.50 volts at idle throttle plate position. The CTS was replaced shortly after the 3.1 engine was installed. I may have even replaced the MAP sensor and I think the O-2 sensor has also been replaced. The IAC was replaced with a new one but didn't resolve the problem. All these were replaced at least a year ago.
The 87 engine that was in the car would immediately start and idle smoothly any time it was started, whether hot or cold. Everything from the old engine was transferred to the current engine but it will not idle at cold start. The idle fluctuates up then down and stalls. The accelerator must be held at high idle until it does go into closed loop and even then it will waver until it reaches near full operating temperature. Once it does, it idles perfectly.
Anyone have any ideas what might be telling the IAC to constantly adjust when it's cold?
I have set the TPS to exactly 0.50 volts at idle throttle plate position. The CTS was replaced shortly after the 3.1 engine was installed. I may have even replaced the MAP sensor and I think the O-2 sensor has also been replaced. The IAC was replaced with a new one but didn't resolve the problem. All these were replaced at least a year ago.
The 87 engine that was in the car would immediately start and idle smoothly any time it was started, whether hot or cold. Everything from the old engine was transferred to the current engine but it will not idle at cold start. The idle fluctuates up then down and stalls. The accelerator must be held at high idle until it does go into closed loop and even then it will waver until it reaches near full operating temperature. Once it does, it idles perfectly.
Anyone have any ideas what might be telling the IAC to constantly adjust when it's cold?