RPM's jump up and down

Tiny
KYLE BAUMGARDNER
  • MEMBER
  • 1990 CHEVROLET 1500
  • 143,000 MILES
The truck listed above c1500 5.0, the rpm's keep jumping up and down from 500 to 1,200 and there is no code coming up at all. What could cause that?
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Thursday, May 21st, 2020 AT 12:47 PM

3 Replies

Tiny
KASEKENNY1
  • EXPERT
I would suggest starting to check for vacuum leaks. There are a number of things that can cause this so let us know what you have done so far. If nothing then I would follow this guide first and let us know what you find and we can go from there.

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

Once we know this we can move on. I attached another guide that talks about high idle which is slightly different but contains things that we will need to run through if there are no vacuum leaks.

https://www.2carpros.com/articles/engine-idles-too-high
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Thursday, May 21st, 2020 AT 5:20 PM
Tiny
KYLE BAUMGARDNER
  • MEMBER
I did, I have checked all lines they are brand new as well.
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Thursday, May 21st, 2020 AT 10:42 PM
Tiny
KASEKENNY1
  • EXPERT
Okay. Let's move onto fuel pressure. Here is a guide for that. We need to see what the fuel pressure is doing when this RPM is ranging like this.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

If you don't have a gauge then you can probably rent one from a parts store. Let me know if you have questions.
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Friday, May 22nd, 2020 AT 7:46 PM

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