Idle surge after swapping throttle body

Tiny
DUSTYROGERS665
  • MEMBER
  • 1993 CHEVROLET 1500
  • 5.7L
  • V8
  • 2WD
  • MANUAL
  • 170,000 MILES
I recently swapped my 1993 throttle body to a 1990(?) Throttle due to the 1993 pouring gas everywhere. I got all the sensors hooked up and it does not want to idle. It's finicky on when it wants to run. When it does, the idle surges hard between 1,000 and 2,000 RPMs giving it a little gas. Keep in mind with the 1993 throttle body, I had a slight surge, maybe 300(+/-) averaging 700-800 RPMs. The idle is so extreme it sounds like it has a huge cam. Gas depressed it shuts off, with the exception of every once in a while it'll bog down to 500. That being said, it drives well as long as the RPMs never goes below 2,000. In gear if I try to drive around 2,000 RPMs it will jerk like its in a gear that to high. Now driving through town at 30 MPH (transmission in 4th gear) RPMs sit at 1,200-1,500 and doesn't surge. I'm stumped, any pointers or suggestions will be appreciated.
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Tuesday, July 20th, 2021 AT 8:38 AM

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Tiny
ASEMASTER6371
  • EXPERT
Good morning,

The throttle bodies are exactly the same.

The surging could be from different things.

https://www.2carpros.com/articles/engine-idles-too-high

1. Fuel pressure. I would check the exact fuel pressure to be sure it is within specs. This is a low-pressure system and only requires 9-13 pounds of pressure. If it is too high, it will cause this and if it is low it will also cause this.

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

2. Vacuum leak. If the engine has a vacuum leak the idle air control will constantly hunt for the correct idle speed and stabilize it. Check all the hoses carefully for any cracks or breaks.

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

3. EGR valve. If the valve is stuck open, it will cause a massive vacuum leak causing this issue. I attached the location and the procedure for removing it. After you remove it, make sure there is no carbon build-up at the end preventing it from seating.

Roy
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Wednesday, July 21st, 2021 AT 1:42 AM

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