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LT1 High Idle , Help Needed

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  • LT1 High Idle , Help Needed

    Hi, My father build a custom wooden boat with a 95-97 Indmar LT1 TBI out of mastercraft prostar. The boat has high idle issues (1200 with correct timing 10deg BTDC), but we have retarded timing in order to get the idle down temporarily.

    Here are the troubleshooting steps. TPS and IAC have been replaced with no difference in the idle. Checked fault codes with an LED, no issues (blinked 12, 5 or 6 times before stopping).

    Initial look at vacuum leaks show no significant issues, but we are going to replace the PCV line as it is a little worn and loose, and will check the TBI plates and gaskets again.

    Any thoughts as to what the issue could be?

    Is there a reset procedure when replacing the IAC?

    Could the engine coolant temperature sensor impact the idle that much? We reset timing and check idle when the engine is fully warm. Although, even with new thermostats and an
    impeller, the idle temperature varies from 140-185 (holds nice at 160 when running).

  • #2
    What value is the tps giving?
    1986 Marlin Magnum Skiier-sold
    1999 Maristar 210VRS-weekend ride
    1996 205 with LT1 cracked block-stitched back together

    Comment


    • #3
      Also has it ever run right since you put it in? What is your fuel pressure and how does the spray pattern look on the injectors.

      As for the IAC you could repark it, the procedure is in the manual.
      1986 Marlin Magnum Skiier-sold
      1999 Maristar 210VRS-weekend ride
      1996 205 with LT1 cracked block-stitched back together

      Comment


      • #4
        LT1 and TBI engines are totally different. Which one do you have? If LT1 you need the tech mate tool or laptop to set the idle. TBI, you can jump the OBD port or get a CodeMate and put the ECM in service mode - you got blink codes - 12 and nothing else. You're commenting like TBI...remember, that TBI unit is from the Chevy 454 and not chevy 350.

        IIRC from my 94 TBI, 10° BTDC, idle 850-900 @ 1000 rpm.
        1993 25th Anniversary Limited ProStar 190, #17

        Comment


        • #5
          No, it has not run properly in this boat yet.

          We can't see a specific value from the TPS, I don't have diagnostic software, yet. It does seem to respond fine to the throttle and we proactively replaced the original TPS as a troubleshooting step (even though it was likely unnecessary).

          Have not specifically checked fuel pressure, but can add that to the list. It does have a new fuel pump (the lower pressure version I believe) and two new injectors that were replaced before it went in the boat (because when testing, the spray on one of them didn't look right, so both were replaced).

          Repark the IAC? We have the Clymer manual, but I don't recall seeing any procedures for this.

          Bret, unless I am missing something, I am fairly positive the LT1 is the Gen II 350 block and heads with reverse flow cooling (dual thermostats 143 and 160deg C). The TBI (throttle body injection) is the version of fuel injection. We have the OBD port, where we jump A and B with a paper clip to put into service mode, and have an LED that attached to two other ports (maybe E and F) for reading codes.

          Comment


          • #6
            Response

            No, it has not run properly in this boat yet.

            We can't see a specific value from the TPS, I don't have diagnostic software, yet. It does seem to respond fine to the throttle and we proactively replaced the original TPS as a troubleshooting step (even though it was likely unnecessary).

            Have not specifically checked fuel pressure, but can add that to the list. It does have a new fuel pump (the lower pressure version I believe) and two new injectors that were replaced before it went in the boat (because when testing, the spray on one of them didn't look right, so both were replaced).

            Repark the IAC? We have the Clymer manual, but I don't recall seeing any procedures for this.

            Bret, unless I am missing something, I am fairly positive the LT1 is the Gen II 350 block and heads with reverse flow cooling (dual thermostats 143 and 160deg C). The TBI (throttle body injection) is the version of fuel injection. We have the OBD port, where we jump A and B with a paper clip to put into service mode, and have an LED that attached to two other ports (maybe E and F) for reading codes.

            Comment


            • #7
              Hi, My father build a custom wooden boat with a 95-97 Indmar LT1 TBI

              LT1


              TBI

              The TBI 350 has standard cooling (old style water pump), you can set timing with computer in service mode. LT1 engine, with coil packs, you need laptop or tech mate to adjust idle.

              What I was saying is the LT1 is not a TBI engine.
              1993 25th Anniversary Limited ProStar 190, #17

              Comment


              • #8
                Originally posted by mattV View Post
                No, it has not run properly in this boat yet.

                We can't see a specific value from the TPS, I don't have diagnostic software, yet. It does seem to respond fine to the throttle and we proactively replaced the original TPS as a troubleshooting step (even though it was likely unnecessary).

                Have not specifically checked fuel pressure, but can add that to the list. It does have a new fuel pump (the lower pressure version I believe) and two new injectors that were replaced before it went in the boat (because when testing, the spray on one of them didn't look right, so both were replaced).

                Repark the IAC? We have the Clymer manual, but I don't recall seeing any procedures for this.

                Bret, unless I am missing something, I am fairly positive the LT1 is the Gen II 350 block and heads with reverse flow cooling (dual thermostats 143 and 160deg C). The TBI (throttle body injection) is the version of fuel injection. We have the OBD port, where we jump A and B with a paper clip to put into service mode, and have an LED that attached to two other ports (maybe E and F) for reading codes.
                Are you 100% sure you got the right injectors?

                IAC repark procedure is in the factory service manual. Download it from the DropBox link on this site.

                As for the TPS value backprobe the sensor. Youtube it if you don't know how. To do it properly and without causing damage go out and buy some push pins. We need to look and see what the value is to know if the throttle is closed or someone has messed around with it.
                1986 Marlin Magnum Skiier-sold
                1999 Maristar 210VRS-weekend ride
                1996 205 with LT1 cracked block-stitched back together

                Comment


                • #9
                  high idle troubleshooting

                  Thanks for the response.

                  I will have to double check on the fuel injectors.

                  By factory service manual, do you mean the Clymer's manual. We have one. If not, could you share the link or directions on how to find it.

                  Yeah, I can double check the tps with a multimeter. We also got a plug to block the air flow to the IAC to help confirm that isn't part of the problem (without a computer).

                  Comment


                  • #10
                    high idle troubleshooting

                    Just checked, the fuel injectors were rebuilt, so that shouldn't be an issue.

                    I found the dropbox. Lots of files I will try to read through in more detail, but one said the IAC reset/repark was just keying on for 10 seconds and then turning off. Will try that too.
                    Simple enough.

                    Unfortunately, due to weather and the boat being a ways away, I won't be able to get to it until next weekend. I have plenty of stuff to try. Will report back with what we find out.

                    Comment


                    • #11
                      Hope you can get it fixed! Great engine onces it's running well.
                      - Jeff

                      1994 205, LT1

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                      • #12
                        So, then is the "TBI" engine a gen 1 style block and heads?

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                        • #13
                          Fixed

                          Fixed.

                          Found a vacuum leak. Found a threaded hole on the front of the TBI unit open causing the vacuum leak. If anyone knows if this is used on a mastercraft, I would be interested to know.

                          Thanks for the help. Looking through the MEFI 2 book on dropbox helped me understand the system better and quickly identify the vacuum leak.

                          Comment


                          • #14
                            Originally posted by mattV View Post
                            So, then is the "TBI" engine a gen 1 style block and heads?
                            Until they went to Vortec heads. They had a proprietary intake manifold, too

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