Intermittent throttle acceleration sticking?

2005 MITSUBISHI ECLIPSE
223,000 MILES • 2.4L • 4 CYL • 2WD • AUTOMATIC
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RBLASCHKE
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I have a recently replaced throttle body assembly which came with the idle sensor and throttle position sensor attached. I have new spark plugs. What's happening is when I push hard on the accelerator pedal the engine will speed up like it's supposed to but when I let off the pedal it does not throttle down. My only fix is to put the car in neutral and then the RPMs will drop on their own or sometimes I have to push the gas pedal down real hard 2 or 3 times and then the RPMs will come down. Then I put it back in drive and keep going. The pedal is not sticking, and neither is the new butterfly in the throttle body assembly. What else could it be?
Sep 24, 2024 at 8:07 AM
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STRAILER
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It could be the throttle cable needs to be replaced and is holding the throttle open or the IAC motor is not working or is working slowly. Do you have a check engine light on? If so, we should run the codes, this guide can help:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

The air must be getting in somewhere, is the throttle body installed on the intake correctly? Here is a guide that shows the common causes of a high idle:

https://www.2carpros.com/articles/engine-idles-too-high

Here is the location of the IAC valve so you can make sure it is plugged in. Check out the images (below). Please upload pictures or videos in your response of any problems so we can see what to help you with.

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Sep 24, 2024 at 3:49 PM
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RBLASCHKE
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There are no warning lights or check engine lights for error codes being displayed. The new throttle body I put on came with an IAC and a TPS. Is it possible a new IAC is defective? I will check the connection. Does the IAC run off of vacuum or is it strictly electrical? I plan on checking vacuum lines this weekend.
Sep 25, 2024 at 7:23 AM
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STRAILER
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Oh yes, it is highly possible the part is defective. In fact, I was going to suggest that. Let me know after you get the replacement part.
Sep 26, 2024 at 11:29 AM