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LS1 surging at idle

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  • LS1 surging at idle

    At the end of my trip yesterday, my engine started surging at idle. Mild built n/a LS1.

    Basically, it surges to around 3000 rpm, then back off to normal idle, surge up and down a couple of times to around 2000, then surge to 3000 again. Keeps cycling like this.

    It's only happening when the engine is warm. It sound like it hunting for fuel or air, I don't know.

    Any ideas where to start. IAC sensor, TPS?

    Possibly bad alternator?

    Thanks for the help.
    Last edited by Grey Mamba; 01-13-2020, 11:07 AM.

  • #2
    i would check for vacum leaks first

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    • #3
      Yes start with vacuum leaks. Possibly clean the IAC
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      • #4
        ok, i'll check for vacuum leaks and Ihave a new IAC to swap out if necessary. I hope it's this simple.

        What's the most likely place to find a vacuum leak?

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        • #5
          for Vacuum leaks, I would start around the intake / injectors... use some starter fluid / carb cleaner and spray around to see if you get a rise in RPM's

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          • #6
            Figure it out ??

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            • #7
              Originally posted by Sand tourS View Post
              Figure it out ??
              Haven't had time to work on it yet. Still in my trailer. I'll report back when I play with it.

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              • #8
                Update: I was in Glamis this weekend and my car was still surging at idle.

                I checked for a vacuum leak, didn't find one. Then I cleaned out the IAC chamber and the entire throttle body. There was a lot of carbon build up in the IAC chamber.

                Put it back together - still surging. Swapped the IAC, still surging.

                While turning the car on and off for testing, I noticed that my car was really struggling to start. Sounded like a dead battery or a starter issue. This has been getting worse over the course of the season, but I figured it was from my batteries not being charged.

                So I did a battery voltage test with the car off - 13V. Also did a battery load test (batteries are good).
                Voltage test battery while car is running (14.5V, alternator is good).

                So I figured it must be the starter. My starter was barely hanging in there and was giving me plenty of notice to replace it. She didn't want to leave me stranded in the dunes! Headed over to Joe Fab and bought a starter from him. Swapped the starter and the car fired right up.

                AND.....my surging idle was gone. The car ran perfectly the entire weekend and the surging never resurfaced. Makes absolutely no sense that the 2 issues were related, right? The car was surging on my way to Joe Fab's shop to get the starter. But I ran all weekend and put it back in the trailer without the surging. Go figure.

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                • #9
                  Crazy, but stoked it ended up that simple of a fix for you! Especially if it made the rest of the weekend worry free!!!

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                  • #10
                    you probably had a bad connection somewhere while messing with the starter you made the loose connection get better . does the computer grab power from the starter battery terminal.

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                    • #11
                      Glad it's solved. Always better to find a 'smoking gun' but take it as a win. I'm sure that starter at Joe's wasn't cheap.


                      If anyone wants a backup starter I have two freshly rebuilt from IMI. I can dig them out of the trailer and get specific model numbers. Pretty sure they are 101N and/or 104. I was going to list them for sale but have been lazy. These are VW style for Mendeola transaxles and will not work on my LS bell housing, which is why I'm selling them all,
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