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Low/rough idle

Tiny
ANZIL001
  • MEMBER
  • 1995 SATURN SC2
  • 2WD
  • 214,000 MILES
I have been trying to find out why my car does not idle properly. When cold it idles okay and when driving there are no problems. I changed the EGR, coolant temperature sensor and connector, cleaned the map sensor and checked throttle position sensor. Looked into the intake and there is quite a bit of carbon build up. I was going to take the intake manifold off and clean it and check the gasket but I would rather not since I its going to be a pain. Any suggestions? Thanks!
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Wednesday, January 31st, 2018 AT 10:13 AM

19 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,662 POSTS
Yes, you are on the right track, choking can cause the problem are you describing. Here is a guide to help you see what you are in for when doing the job:

https://www.2carpros.com/articles/throttle-actuator-service

Please let us know what you find. We are interested to see what it is.

Cheers, Ken

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Friday, February 2nd, 2018 AT 11:57 AM
Tiny
ANZIL001
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  • 11 POSTS
Unfortunately I already did that and still no luck. I plan on putting the injector cleaner in and spraying some throttle body cleaner into the intake while the car is running to break up the deposits in the intake manifold. Do you think this would help or not? Thanks!
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Saturday, February 3rd, 2018 AT 5:44 PM
Tiny
KEN L
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You could have low compression in one cylinder causing the issue as well can you do a compression test by following this guide?

https://www.2carpros.com/articles/how-to-test-engine-compression

Please let us know what you find.

Cheers, Ken
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Sunday, February 4th, 2018 AT 11:35 AM
Tiny
ANZIL001
  • MEMBER
  • 11 POSTS
Compression test seemed like it checked out fine. Standing in front of the car going from left to right: cylinder 1- 190psi, 2-200, 3-200, 4-200. Spark plugs looked good as well. I made sure to pull the fuel pump fuse and relay as well as the wires going to the distributor. When I started it back up, the rpms shot up to 4000 before I turned it off. I tried it again and same thing. Not sure whats next. Thanks!
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Tuesday, February 6th, 2018 AT 6:42 PM
Tiny
KEN L
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The compression is great, what did the spark plugs look like can you shoot a picture of them and upload it? It sounds like you may have a bad fuel injector and seeing the plugs will tell us which cylinder.
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Wednesday, February 7th, 2018 AT 10:47 AM
Tiny
ANZIL001
  • MEMBER
  • 11 POSTS
Spark plugs looked fine, a nice dry light brown/tan color. There was some oil around the plug area though. I could snap a picture when I get home.
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Wednesday, February 7th, 2018 AT 11:11 AM
Tiny
KEN L
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Have you run the codes? It would be a good idea to see if anything comes up.

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

Please let us know
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Thursday, February 8th, 2018 AT 9:25 AM
Tiny
ANZIL001
  • MEMBER
  • 11 POSTS
All it showed was code 12 which I think means there are no codes. Tried starting it again and rpms wend right back up to 4000
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Friday, February 9th, 2018 AT 10:07 AM
Tiny
KEN L
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We are getting closer. I think you have a IAC motor that is dirty or needs replacement.

Here are diagrams to help you remove and replace the unit.

Please let us know what you find.

Cheers, Ken
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Friday, February 9th, 2018 AT 10:30 AM
Tiny
ANZIL001
  • MEMBER
  • 11 POSTS
Ok, That was one of the parts I cleaned. Do you think just replacing the whole thing would make a difference? Thanks!
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Friday, February 9th, 2018 AT 10:45 AM
Tiny
KEN L
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Yep it should, but first run this vacuum leak test.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

and

https://youtu.be/4ktw1X4W_-k

Please let us know

Cheers, Ken
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Friday, February 9th, 2018 AT 12:55 PM
Tiny
ANZIL001
  • MEMBER
  • 11 POSTS
I found this fuel line thay was gummed up with this orange waxy stuff. Not sure what this goes to but im going to look more into it. As far as the vaccum test, I cant spray the carb cleaner anywhere since the engine rpms are too high. If I need to get a tester I can. Its just weird that this wasnt my original problem so it probably has something to do with me cranking the engine with the fuel relay and fuse out.
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Friday, February 9th, 2018 AT 3:04 PM
Tiny
ANZIL001
  • MEMBER
  • 11 POSTS
That line was going to the charcol vapor canister. I cleaned the line out. Not sure if this would effect anything
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Friday, February 9th, 2018 AT 3:36 PM
Tiny
ANZIL001
  • MEMBER
  • 11 POSTS
So I cleaned that and also bought a new throttle body gasket. Its running like before with the vairiable idle to almost a stall when it warms up. No more high rpms. I did the leak test and couldnt find anything. Any idea on what to do next? Thanks!
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Saturday, February 10th, 2018 AT 5:36 PM
Tiny
KEN L
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I had an idea that it might be a sticking EGR valve. Here is a video showing you how to check the valve and a diagram on its location.

https://youtu.be/DqUCbbKdWf4

Please let us know what you find.

Cheers, Ken
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Monday, February 12th, 2018 AT 9:17 AM
Tiny
ANZIL001
  • MEMBER
  • 11 POSTS
I wish but I already replaced that. So maybe the IAC?
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Monday, February 12th, 2018 AT 9:40 AM
Tiny
KEN L
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Yep that is where I was going next. Let me know what happens.
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Monday, February 12th, 2018 AT 10:28 AM
Tiny
ANZIL001
  • MEMBER
  • 11 POSTS
So I replaced the IAC and started up and idle just back up to 3-4000 rpm’s again. Please help!
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Wednesday, February 21st, 2018 AT 6:51 PM
Tiny
KEN L
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Can you disconnect the throttle cable from the throttle bore and start it up to see what happens?
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Thursday, February 22nd, 2018 AT 11:28 AM

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