Rough idle at start when hot?

Tiny
DCOURSEN
  • MEMBER
  • 2004 DODGE STRATUS
  • 3.0L
  • V6
  • 2WD
  • MANUAL
  • 96,000 MILES
My car is actually a 2004 Dodge Stratus R/T 3.0L with a 5-speed manual transmission. For the last month or so, I have been having an issue when the vehicle is at operating temperature. The car starts but idles very erratically and eventually stalls. If I play with the gas pedal (pumping it periodically) it will eventually even out and run correctly most of the time. This only happens at operating temperature. When the engine is cold, it starts and runs fine. The car also does not throw any codes. When this happens nor have I noticed a drop in mileage (pretty consistently 19 MPG city), which I find odd because clearly it is not running right. I am thinking it is a vacuum or temperature sensor problem but am not sure where to start or even if I am correct. Any ideas would be welcome.
Thursday, November 10th, 2022 AT 5:37 PM

7 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 51,537 POSTS
Yep, good call, a vacuum leak, engine coolant sensor or bad MAF sensor can cause this without throwing a code. I would check for a vacuum Leka first then try the MAF sensor. Here is a guide to help you check for a vacuum leak (engine cold only) and the locations of the sensors as well in the images below.

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

Check out the images (below). Please let us know what you find. We are interested to see what it is.
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Friday, November 11th, 2022 AT 10:15 AM
Tiny
DCOURSEN
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  • 4 POSTS
Thanks for the info. I will have to get into this on the weekend as I am too busy during the week. I'll let you know what happens.
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Tuesday, November 15th, 2022 AT 9:07 AM
Tiny
KEN L
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Sounds good, let me know.
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Wednesday, November 16th, 2022 AT 1:26 PM
Tiny
DCOURSEN
  • MEMBER
  • 4 POSTS
I've done a little more research into this and it seems to be pointing me away from a vacuum leak. If I had a vacuum leak, wouldn't it be difficult to start all the time, not just when it's hot?

I am not sure what I can do about testing the coolant temp sensor or the MAF sensor. It seems to me the only way to verify if one of those are the problem is to put a new one in and see if it corrects the problem.

Is that your assessment as well?
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Friday, November 18th, 2022 AT 11:04 AM
Tiny
KEN L
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  • 51,537 POSTS
Yep, a vacuum leak can affect the engine starting either how or cold depending on the volume of the leak.
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Friday, November 18th, 2022 AT 3:39 PM
Tiny
DCOURSEN
  • MEMBER
  • 4 POSTS
Okay. Then here's my problem. I can't seem to figure out where to hook up the vacuum gauge. I looked in the maintenance manual but it was less than helpful. Do you have any knowledge specific to this vehicle about which line I should be testing? My problem is people have shown me a schematic of the vacuum system but I'm not certain where any of these lines are on the car.
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Saturday, November 19th, 2022 AT 7:44 AM
Tiny
KEN L
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Did you check out the link above it shows you how to check for a vacuum leak.
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Sunday, November 20th, 2022 AT 12:13 PM

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