Idling/running too high

Tiny
THOMAS2270
  • MEMBER
  • 2001 CHEVROLET CAVALIER
  • 2.4L
  • 4 CYL
  • 2WD
  • MANUAL
  • 215,000 MILES
I start the car and it jumps up to 2,000 RPMs, it also is affecting it when it’s in gear. I can put it into gear and not hit the throttle and the car will slowly accelerate. I currently have no codes being thrown and I have had a computer hooked up and ran all sorts of tests (the only way I could lower the idle was by manually changing the idle speed on the computer). I have checked good for vacuum leaks, replaced MAP sensor, cleaned IAC valve, checked Throttle Control Sensor, checked all fuses, and more. Does anybody have an answer or advice?
Sunday, April 17th, 2022 AT 1:44 PM

14 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

This vehicle has a throttle cable. Are you certain it isn't frayed and causing the throttle body not to return to the closed position?

Do me a favor. Disconnect the throttle cable at the throttle body and see if the RPMs go to normal.

Let me know.

Joe

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Sunday, April 17th, 2022 AT 9:42 PM
Tiny
THOMAS2270
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I will run that test, I do believe the throttle body does return to the close position but it’s worth a shot.
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Monday, April 18th, 2022 AT 3:56 AM
Tiny
THOMAS2270
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  • 9 POSTS
I disconnected the throttle cable and there was little to no change. I’ve had some people suggest looking at the ambient air sensor and the cam sensors so I’m going to check those out next. Anymore suggestions or advice?
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Monday, April 18th, 2022 AT 1:07 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Since the IAC has been replaced without change, I need to know if you checked where it mounted to make sure there was no carbon or dirt that could prevent it from moving properly.

Also, I have attached testing procedures for the IAC circuit. Take a look through them and let me know if they help.

Let me know.

Joe

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Monday, April 18th, 2022 AT 8:41 PM
Tiny
THOMAS2270
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  • 9 POSTS
I did check and cleaned where the IAC was mounted, also did a sea foam cleaning which gets sprayed directly into the throttle body so it’s pretty clean, but I will go through those procedures and see if that has an effect.
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Tuesday, April 19th, 2022 AT 5:24 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

Let me know what you find when going through the diagnostics I attached above. Also, if you have a live data scan tool, let me know what the short-term fuel trims are.

I'll watch for your reply.

Joe
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Tuesday, April 19th, 2022 AT 5:12 PM
Tiny
THOMAS2270
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  • 9 POSTS
I don’t have the proper tools to run all those tests, but I was messing with the IAC (manually changing how far it came out) and I did get it to lower to about 1,300 RPMs. And then when I started it up again it shot back up above 2,000. So, I’m going to replace that today and run some tests on the computer and see if that will fix it.
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Wednesday, April 20th, 2022 AT 7:20 AM
Tiny
THOMAS2270
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  • 9 POSTS
I replaced the IAC and there was no change, I can manually pull the valve out and install the valve, and it will run just above where it’s supposed to be. But when I start it up again it will shoot up to 2,000, I can manually adjust it and not plug the valve in and it will run fine.
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Wednesday, April 20th, 2022 AT 10:20 AM
Tiny
THOMAS2270
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I feel dumb, but I do have a vacuum leak coming from my intake, I’m guessing it’s the gasket so when I get that torn apart I’ll let y’all know if that is it for sure.
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Wednesday, April 20th, 2022 AT 1:22 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

It sounds like you found the problem, and please don't feel dumb. That is a really easy thing to miss. Remember, this is a plastic intake so be careful.

I attached the directions for removal and replacement. The directions include torque specs as well.

Let me know if this takes care of the issue.

Take care,

Joe

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+1
Wednesday, April 20th, 2022 AT 8:19 PM
Tiny
THOMAS2270
  • MEMBER
  • 9 POSTS
I replaced the intake gasket, and it did lower the idle, it now averages about 1,100 RPMs. The idle does surge and fluctuates, it will go as low as 900-1,000 and as high as 1,400- 1,500. I was wondering if y’all had any ideas on how to fix that, I found no vacuum leaks. It is throwing an EVAP code but I’m not sure if it would cause that. The car is definitely drivable, I just want to get it to 100%.
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Sunday, May 1st, 2022 AT 6:24 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

If there is a leak in the EVAP, it can possibly cause an engine vacuum leak. What code is it? Also, let me know what has been done so far to eliminate the EVAP code.

Take care,

Joe
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Sunday, May 1st, 2022 AT 6:42 PM
Tiny
THOMAS2270
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P0440... And I haven’t done anything yet, I was told I would need a smoke test to properly diagnose what needs fixed, I figured I would ask before I just started replacing stuff.
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Monday, May 2nd, 2022 AT 8:53 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

The code indicates the EVAP is unable to achieve or maintain a vacuum during the diagnostic test. So certainly, there is a leak that is likely causing the idle issues.

A smoke test is what I would do first. If there is a leak, it will show smoke where it is located.

I attached the diagnostics below specific to the code. Take a look through them and let me know if you are comfortable performing them.

Take care,

Joe

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Tuesday, May 3rd, 2022 AT 3:49 PM

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