Car has rough idle and stalls after high rev of RPM's

Tiny
NICKOLASMIKE
  • MEMBER
  • 2004 GMC YUKON
  • V6
  • AUTOMATIC
  • 196,000 MILES
So I have the vehicle listed above Denali, it has been sitting about 8 months ran fine when I left it there but anyways. I tried to crank it and gad to have it jumped off to crank it I replaced the alternator. Still the problem persists. It will crank and run for about 6 or 7 minutes at rough idle without hitting gas. However I could rev it up all day and it act just fine until I let off gas it stalls when it gets to lower RPM's. I have no idea what could be the problem.
Tuesday, October 27th, 2020 AT 5:28 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

Have you checked to make sure none of the vacuum hoses have been damaged by mice or other things? I don't know if it sat outside, but if it did, that's a possible issue.

Take a look through these links and let me know if they help:

https://www.2carpros.com/articles/stall-at-idle

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

There are other things as well that can cause this. However, start with these and let me know if it is something you have already done or if you have other questions.

Take care,
Joe
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Tuesday, October 27th, 2020 AT 6:21 PM
Tiny
NICKOLASMIKE
  • MEMBER
  • 7 POSTS
So I did what you said found no leaks. Mind you vehicle has been sitting so I cleaned throttle body and it will idle good now and not cut off however I am getting an engine code stating random cylinder misfire any idea what could cause this?
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Thursday, October 29th, 2020 AT 4:47 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
It could be a few things. If you clear the code, does it come right back? A random misfire can result from a few different things. For example, a deviation in fuel pressure from the manufacturer's specs, a weak coil. Is the P0300 the only code you get?

Another thing to consider is engine compression. With the mileage on the vehicle, there is a chance one or more of the cylinders is weak.

Let me know. Also, let me know if you have a live data scan tool. If you do, let me know the short term fuel trims.

Take care,
Joe
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Friday, October 30th, 2020 AT 4:42 PM

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